How We Produce Impact Estimates

Published: November 2021; Last updated: January 2025
(February 2024 version, July 2023 version, April 2023 version, July 2022 version, November 2021 version)

General philosophy

When we’re communicating impact, we strive to adhere to the following principles:

• Be accurate. Don’t misrepresent or imply that a donation will accomplish more (or less) than we expect it to.
• Be clear. To the extent possible, make straightforward claims that are easy to understand.
• Don’t imply a false level of precision. While models may provide estimates down to the dollar, round them so they don’t suggest we believe in that level of specificity.
• Share the work with those who want it. Make the detail behind impact estimates available for anyone who wants it.

How we generate impact estimates

Impact metrics for grants to GiveWell’s Top Charities

We use the inputs below on our Top Charities page and other estimates of impact. You can see more detail in this spreadsheet.

Intervention	Top Charities implementing this intervention	Outcome	Cost of outcome (2021-2023 average, rounded up to nearest $500)	Output	Cost of output (2021-2023 average, rounded to nearest dollar)
Malaria nets	Against Malaria Foundation	Lives saved	$5,500	Number of nets delivered to households	$5
Malaria medication	Malaria Consortium	Lives saved	$4,500	Number of children treated with a full course of medicine	$7
Incentives for immunizations	New Incentives	Lives saved	$4,500	Number of infants vaccinated who would not have been vaccinated without the program	$148
Vitamin A supplementation	Helen Keller Intl	Lives saved	$3,500	Number of children receiving supplements	$2

For life-saving programs, we present two cost-effectiveness estimates: one based on the cost of each output and one based on the cost of each outcome. Outcomes refer to the ultimate impact of the donation, such as saving a life, that results from the outputs. Outputs refer to the measurable activities a donation generates, such as treating a child with a full course of malaria medication, which in turn lead to the outcomes.

Our cost-per-output estimates are based on financial and programmatic information from our Top Charities. When estimating total outputs attributed to a specific amount of funding (e.g., how many nets will $100 deliver?), we divide the total funding by our estimate of how much it costs to deliver that output (e.g., how much it costs to deliver an insecticide-treated net).

For both outcome and output estimates, we use a weighted average of the cost-effectiveness for funds we directed to specific funding opportunities in the most recent calendar year. We use a weighted average because both cost per output and cost per outcome vary among programs we recommend funding for. For example, we made both of the grants below to Malaria Consortium’s seasonal malaria chemoprevention program in March 2024:

• $9.9M to distribute malaria medication in Borno, Nigeria at a cost of $6 per child treated with a full course of medicine, resulting in an estimated cost-effectiveness of around $3,500 per life saved
• $2.0M to distribute malaria medication in Togo at a cost of $12 per child treated with a full course of medicine, resulting in an estimated cost-effectiveness of $6,500 per life saved

Cost-per-life-saved estimates have been rounded up to the nearest $500, and cost per output estimates have been rounded to the nearest dollar. Our impact estimates include a weighted average of all grants we made to each program. You can see a list of the specific funding opportunities used in these calculations by looking at grants approved in February 2021 through January 2024 in this spreadsheet. We categorize grants by year according to the date we decided to make or recommend them, not the date funds were disbursed. Our impact numbers don’t include all funds we direct to our Top Charities. More detail on this below.

Lifetime impact of GiveWell-directed donations to Top Charities

From 2009 to 2023, GiveWell directed a total of $1.15 billion to our current Top Charities.1 We estimate that this funding will save a total of about 270,000 lives by:

• Distributing 76.6 million insecticide-treated nets to households
• Treating 65.2 million children with a full course of anti-malarial medicine
• Providing vitamin A supplements to 120.7 million children
• Vaccinating 921,000 infants who wouldn’t have been vaccinated otherwise

To estimate the overall impact of GiveWell-directed donations to Top Charities, we make a couple of assumptions.

• We assume funds directed to Top Charities that are difficult to attribute to specific funding opportunities are about as cost-effective as the average dollar directed to each organization in 2021 (see table here).2 We make this simplifying assumption because we estimate the cost-effectiveness of donations at the funding opportunity level (see below), and it would be difficult to guess how cost-effective these types of donations will be without knowing which specific programs they will be spent on. We make the same assumption for grants to Top Charities for which we didn’t create cost-effectiveness analyses. This includes grants to fund our Top Charities’ activities beyond standard program implementation, such as scoping grants. We can think of reasons to guess that these types of funds may tend to be more or less cost-effective than the average donation.3 In the absence of more information, we expect them to be roughly equally cost-effective overall.
• We assume funds directed to Top Charities in 2009 to 2019 were about as cost-effective as the average dollar directed to each program in 2021 (see table here).4 We make this simplifying assumption because we have not retroactively calculated the impact of individual grants from before 2020. Because we think it’s likely that the cost-effectiveness of our Top Charities’ programs has been decreasing over time, we believe this is a conservative assumption that may underestimate the true impact of GiveWell-influenced donations.

What funding does GiveWell look at to calculate cost-effectiveness?

Funds directed to our Top Charities by GiveWell can be grouped in five buckets:

1. Grants we make from our Top Charities Fund and All Grants Fund to specific funding opportunities
2. Grants we make from GiveWell’s pool of unrestricted funding. See our excess assets policy
3. Donations we recommend large donors make to specific funding opportunities
4. Donations that donors make to an organization we recommend, but that aren’t directed to a specific funding opportunity. This includes donations made to organizations through our donation portal, donations made directly to the organizations, and donations through other third-party organizations that share GiveWell’s recommendations (e.g., One for the World).

We calculate the cost-effectiveness of specific funding opportunities, not the cost-effectiveness of all the funding an organization uses. Because of this, we are only using buckets 1 through 3 as the basis for calculating the cost-effectiveness numbers we’re using in our impact estimates. This constitutes the majority of the total funding we direct to each Top Charity.

We exclude the funding in bucket 4 from our impact calculations because we don’t have estimates of the cost-effectiveness of those donations. We only calculate the cost-effectiveness for specific funding opportunities. Funding directed to our Top Charities could be either more or less cost-effective than the funding directed to specific funding gaps. Rather than guessing at a number and using it for our calculations, we’ve excluded this funding.

We also exclude grants for which we don’t generate a cost-effectiveness estimate. For example, we do not estimate the cost-effectiveness of grants for monitoring surveys to assess the success of programs. These improve our decision-making ability, but don’t have a direct impact.

We do include these types of funding in our lifetime impact estimates (see above).

What are funding opportunities?

GiveWell makes its decisions about where to recommend funding based on estimates of the cost-effectiveness of specific “funding opportunities” rather than the entire portfolio of an organization’s work.

A funding opportunity is generally defined as a specific intervention (e.g., seasonal malaria chemoprevention) in a specific country, although funding opportunities may also be defined at the subnational level.

Our cost-effectiveness estimates can differ between funding opportunities. For example, in our April 2024 cost-effectiveness analysis for Malaria Consortium’s seasonal malaria chemoprevention program, we estimated that the program in Burkina Faso was roughly twice as cost-effective as its work in Chad, largely driven by higher rates of malaria mortality in Burkina Faso.

Why does GiveWell calculate cost-effectiveness at the funding opportunity level?

We analyze individual funding opportunities rather than programs or organizations as a whole because we believe it allows us to better distinguish between different uses of marginal funding. If we directed funding based solely on a single organization-level cost-effectiveness estimate, our analysis would result in recommending funding to only one organization.

We believe that would be misleading and would lead to less cost-effective grant-making. By estimating cost-effectiveness at a more granular level, we are better able to recommend funding to multiple programs and direct funding to the most cost-effective opportunities on the margin. We use these estimates to decide how to allocate funding from the Top Charities Fund.

As well as estimating the cost-effectiveness of specific funding opportunities, we also present aggregate cost-effectiveness estimates for each program on our Top Charities page.

How are numbers rounded?

You can see a list of the specific funding opportunities used in these calculations here.

The cost-effectiveness estimates we share for specific funding opportunities don’t exactly match the numbers we’ve shared in the table above. We’ve rounded the numbers to avoid giving a false sense of precision.

• We’ve rounded cost-per-life-saved estimates up to the nearest $500.
• We’ve rounded cost-per-output numbers to the nearest dollar (up or down).

For example, you can see in the linked sheet that the cost-effectiveness of our life-saving Top Charities can vary by hundreds of dollars. We don’t think our models are precise enough to actually differentiate between differences in cost-effectiveness of only a few hundred dollars, so we’ve rounded estimates up to the nearest $500 to better convey this.

How often does GiveWell update impact numbers?

We update our impact estimates annually to incorporate grants from the preceding metrics year (our metrics year runs from February 1 to January 31).

Does GiveWell recalculate past cost-effectiveness estimates regularly?

We finalize our cost-effectiveness estimate for any given funding opportunity shortly before we make the grant to that opportunity (or recommend it to a third party). We don’t go back and update these estimates when our cost-effectiveness model changes. We think it would impose a large administrative burden without substantially improving our decisions for upcoming grants. This means that we may reach a different estimate of cost-effectiveness for some past grants if we were to re-evaluate them now.

Guidance for interpreting impact estimates

Why is the cost to save a life so high?

We often get questions about why we estimate it costs thousands of dollars to save a life if, for example, it only costs approximately $5 to distribute a malaria net, or $7 to distribute antimalarial medicine, or $2 to provide a year’s worth of vitamin A supplements to a child—some of the interventions we recommend to save lives. It’s not intuitive!

We explain our estimate of the cost to save a life is higher than our estimate of the cost per treatment or item on this page.

What are marginal funding and marginal impact?

Marginal funding is the last funding that goes to a program. It’s important because the impact of marginal funding is often different from the average impact of funding to a program.

For example, imagine that the Against Malaria Foundation is considering funding the distribution of insecticide-treated nets in Nigeria. They have identified two areas as excellent candidates for distribution:

• They could distribute $1 million worth of nets in areas with the highest rates of malaria. This would save 200 lives at the cost of $5,000 per life saved.
• They could distribute an additional $2 million worth of nets in areas with lower rates of malaria. There is less malaria to prevent, so it costs a bit more to save lives. This distribution will save 250 lives at the cost of $8,000 per life saved.

The average cost to save a life with this program if fully funded with $3 million would be about $6,700 per life saved.

But that wouldn’t be the impact of your donation. Your donation would go to one area or the other. If AMF had already raised $1 million before you gave, they would spend it in the areas with the highest malaria prevalence. If you gave after that, your donation would go to the areas with lower malaria prevalence where it cost $8,000 to save a life.

We call this last donation marginal funding. The marginal impact is what your donation actually causes to happen.

Rather than trying to estimate the marginal impact of each dollar, GiveWell typically estimates the marginal impact of giving to a program’s funding opportunities. These typically refer to a pool of funding directed to a program in a single country or subnational region. We estimate the cost-effectiveness of each funding opportunity, and regularly reassess what marginal donations will accomplish based on which funding opportunities an organization will spend on next.

What is funging, and how does it affect impact?

When you give, you impact how GiveWell allocates funding from other donors. So even when you give to a specific program, the impact of your donation may be felt elsewhere based on how GiveWell ultimately allocates its full pool of funding. We call this funging (from fungibility).

For example, imagine that GiveWell has identified two excellent funding opportunities:

• An opportunity with Helen Keller Intl is the most cost-effective, and needs $5M to distribute vitamin A supplements.
• An opportunity with Against Malaria Foundation (AMF) is the next most cost-effective, and needs $20M to distribute malaria nets.

GiveWell has $15 million available to direct wherever it deems best. You decide to donate $50 to Helen Keller Intl’s vitamin A supplementation program.

Because GiveWell will fully fund the most cost-effective opportunity first, your donation effectively moves $50 of GiveWell’s dollars from Helen Keller Intl to AMF. GiveWell doesn’t have to give that $50 to Helen Keller Intl — you’ve already provided it.

Each year, GiveWell recommends several hundred million dollars in grants to specific funding opportunities that GiveWell chooses. With that much funding, many donors who choose to give to a specific program will effectively have their donation increase the budget of a different organization.

Note that there are different kinds of funging. The above only refers to how donations directed to an individual Top Charity displace other GiveWell-directed funds. Our estimates also attempt to incorporate the possibility that our Top Charities displace funds for an intervention from other sources (e.g., governments).

Why does GiveWell share the impact of grants rather than donations?

Sharing the impact of donations is challenging because individual donations to particular programs can be funged by GiveWell (see above). Because we don’t know the ultimate impact that a given donation will cause through funging, any estimate we shared based on the immediate recipient of the donation would likely be inaccurate.

To avoid sharing potentially misleading estimates, we share the impact of grants from the pool of funding we direct to funding opportunities. Because grants don’t displace other GiveWell-directed funding, this allows us to share estimates we’re more confident in. It also gives donors the estimate we think they’re looking for — the impact a certain amount of funding has with that program (without taking funging by GiveWell into account).

Why does GiveWell show past cost-effectiveness rather than projected cost-effectiveness?

Because we finalize the cost-effectiveness estimates of funding opportunities at the time we recommend a grant, we don’t have estimates for the cost-effectiveness of future grants. Our best guess is that they’ll be similar to past grants, but will become less cost-effective over time. This may happen quickly if GiveWell sees a rapid increase in funding we direct, as we will fully fund the most cost-effective opportunities first.

We believe sharing the past estimated impact gives donors a useful proxy for what their impact may be without making potentially misleading statements about the future.

An idealized version of the Top Charities page would present an aggregated (charity-level) cost-effectiveness estimate based on an up-to-date best guess of how incoming funds would be allocated on the margin. For example, if we believed the next $5 million of funding for Malaria Consortium would be spent in Burkina Faso, and the $5 million after that would be spent in Chad, we would present the cost-effectiveness estimate for Burkina Faso until $5 million was donated, and then present the cost-effectiveness estimate for Chad until the next $5 million was donated, and so on.

However, we believe this approach would be impractical:

• It would be confusing if our impact estimates frequently changed.
• Keeping an up-to-date estimate of how marginal funds would be spent would create an unnecessary administrative burden. Instead, we make decisions about how to allocate funds on a rolling basis, and prioritize a detailed understanding of how we expect marginal funds to be spent for the most decision-relevant funding opportunities.
• It can be challenging to communicate clearly about what we mean by “the margin.” When making decisions about how to allocate funding, we estimate the marginal dollar based on a projection of how much funding organizations will receive from other sources (including donors who give to a specific program on the basis of GiveWell’s recommendation) between now and when the funds will be needed, as well as in the past. For example, based on the example above, if we projected that donors would give $7.5 million to Malaria Consortium, we would expect the marginal additional dollar to be spent in Chad, rather than Burkina Faso. However, that would mean never presenting the cost-effectiveness estimate of Burkina Faso, which we believe would be misleading.

Because of these difficulties, we use a weighted average of programs that GiveWell has directed funds toward in the past several metrics years rather than the cost-effectiveness of the specific opportunity we expect would be funded by a marginal donation. We think this is a clearer way to present a rough and intuitive estimate of how much good a donation can accomplish (which is the goal of the Top Charities page).

Do these cost-effectiveness estimates include all factors that are relevant for choosing which programs to fund?

The purpose of our cost-effectiveness analyses is to help GiveWell make better decisions about how best to allocate funds between different programs.

These estimates abstract from certain features of a program that we think are relevant for choosing which programs to fund. For example, our estimates do not include:

• Our assessment of an organization’s ability to respond effectively to unexpected events
• The costs and benefits of delaying a decision to preserve the value of retaining future options

Because of these limitations, a cost-effectiveness analysis is not the only tool we use when we decide whether to allocate funding to a program. You can see the principles we follow to allocate funding on this page.

In addition to excluding certain factors that we take into account in our decision-making, our cost-effectiveness estimates are often highly uncertain.

While we make our best effort to produce a reliable estimate, it can be challenging to ensure internal consistency between different estimates. For example, for practical reasons we restrict the scope of our estimates to focus on the most important benefits of a particular program.

You can find more information on what goes into our cost-effectiveness estimates here.

Why does GiveWell compare programs to cash transfers?

When we’re making decisions about which programs to fund, we use a single unified metric that compares cost-effectiveness to GiveDirectly’s cash transfer program.5 We often model different types of benefits from an intervention, such as improved long-term economic outcomes for children who are protected from malaria. The “x cash framework” allows us to aggregate a program with different types of modeled benefits into a single metric, which is useful for our decision-making.

An additional benefit of using this metric is that we could spend large amounts of money on direct cash transfers, as the program is relatively straightforward to implement and GiveDirectly has the infrastructure to put significant increases in funding to use. Because of this, cash transfers to GiveDirectly set a clear lower bound on cost-effectiveness that GiveWell should consider (although in practice we aim to fund programs that we believe are substantially more cost-effective than cash transfers; see here for more information).

Despite the benefits of comparing programs to cash transfers, this metric is especially unintuitive. For ease of interpretation, we therefore present our impact estimates in terms of the main benefit from a charity's program.

Is the program with the lowest average cost per life saved the best program GiveWell recommends?

The average cost to save a life differs among our Top Charities and may change from year to year. However, we don’t believe that the organization with the lowest average cost per life saved is a better giving opportunity than our other recommendations, even though these estimates might suggest that.

When we are deciding how to allocate funding to our Top Charities, our research team decides which program has the highest priority funding needs at that time. This decision takes into consideration factors such as:

• Which funding gaps we expect to be filled and unfilled
• Each organization’s plans for additional funding
• The cost-effectiveness of each funding gap

An organization with a lower average cost per life saved may not, for example, have the capacity to absorb funding for additional cost-effective opportunities. For this reason, we don’t believe that donations to the organization with the lowest average cost per life saved are necessarily more cost-effective than donations to our other Top Charities.

• 1

  This only includes funding to our current Top Charities through the end of our 2023 metrics year (which ended January 31, 2024). See the totals here.

  As of December 2024, we had directed more than $2.4 billion to all organizations and grants we’ve recommended, according to the historical metrics reports listed in our 2023 metrics report (in the spreadsheet here), and internal records from 2024.

• 2

  While we have now updated our analysis of the impact of our grantmaking to include some information about funds directed since 2021, we have not yet assessed whether to update our cost-effectiveness estimates for pre-2020 funds directed to rely on these newer cost-effectiveness estimates.

• 3For example, we may expect that donations given directly to organizations on the basis of our recommendations may be used to fund opportunities that we decided weren’t cost-effective enough for us to make a grant to. On the other hand, because we account for the direct donations we expect a program to receive in our analyses of room for more funding, we often assume that these donations will be used to fill the highest-priority and most cost-effective funding opportunities first, and therefore that any grants we make to fill remaining funding gaps would be allocated to relatively lower-priority and less cost-effective funding opportunities.
• 4

  While we have now updated our analysis of the impact of our grantmaking to include some information about funds directed since 2021, we have not yet assessed whether to update our cost-effectiveness estimates for pre-2020 funds directed to rely on those newer our cost-effectiveness estimates.

• 5

  Note that we recently re-evaluated the cost-effectiveness of GiveDirectly’s program and now estimate that the program is 3 to 4 times more cost-effective than we previously estimated (see this blog post for more information). We want to provide the time and attention needed to think through the implications of this change for our benchmark. Until we have thought this through, we will be using our historic benchmark. For now, you can think of our benchmark as “GiveWell’s pre-2024 estimate of the impacts of cash transfers in Kenya,” with GiveDirectly’s current programs in various countries coming in at 3 to 4 times as cost-effective as that benchmark.