Putting a number on a supporter
Let's say the uncomfortable part first. A person who signs up for your newsletter because your work moved them is not a dollar figure, and nobody who does this job well thinks about them that way. The number this page produces is not a judgment about a human being. It is a number you have to hand to a machine, because Google Ads will not run on gratitude.
That is the honest framing. Performance Max, Demand Gen, and every conversion value bidding strategy Google offers need a value attached to each conversion, and if you do not supply one, the system treats every newsletter signup as identical to every $500 donation and optimizes toward whichever is cheapest to buy. Giving it a defensible number is not reducing your supporters to line items. It is the opposite: it is the only way the ad platform learns that the people who sign up for your emails are worth pursuing at all.
How the math works
The usual advice, the one most consultants give, is to divide the total donations from your subscribers by the number of subscribers. It is a reasonable starting point and it is what most nonprofits should do first. But it answers a slightly different question than the one you are asking. It tells you what your average existing subscriber produced last year. What you need for a conversion value is what a brand new subscriber will produce over the years ahead, and those differ in three specific ways.
First, your current list already contains your donors, including your loyal ones, and their gifts get credited to email whether or not email caused them. Second, an annual figure is not a lifetime figure: subscribers stay on your list for years, and any per-year number has to be extended across the time they actually stay. Third, and most important, donor retention is not one number. So this calculator runs the cohort math forward, runs your list history backward as a cross-check, and shows you both.
The formula
And donor lifetime value, done properly, is not average gift times some guessed lifespan:
The share still giving is 100% in year 1, your first-year donor retention rate in year 2, and then multiplied by your repeat donor retention rate for every year after. d discounts future gifts back to today's money. Year 1 is not discounted, because that gift arrives now.
Worked example
A mid-sized nonprofit: average gift $75, 1.6 gifts a year, 8% lost to processing and fundraising costs, 20% first-year donor retention, 60% retention after that, over 5 years at a 5% discount rate.
A donor gives $120 a year, or $110.40 net. The retention curve produces 1.44 giving years, so a donor is worth $154.24 in today's money.
3% of new subscribers eventually give, measured across 1,200 signups. So one signup is worth 3% × $154.24 = $4.63. Because that 3% came from a real sample, the honest range is 2.17% to 4.13%, or $3.35 to $6.36 per signup.
The cross-check: $30,000 of email-attributed giving against 15,000 subscribers is $2.00 each per year, net of costs, extended over 2.85 expected years on the list at 25% churn, equals $5.24. The two methods land 12% apart, which is close enough to bid on the cohort figure with confidence.
The first-year cliff, and the number it quietly breaks
The Fundraising Effectiveness Project, run by the Association of Fundraising Professionals with the Urban Institute, has reported the same uncomfortable pattern for years: overall donor retention sits in the low 40s, while first-time donor retention sits near 20%. Roughly four out of five first-time donors never give a second gift. Meanwhile, donors who have already given twice retain at far higher rates.
Blend those into one number and you get something like 43%, which describes nobody. Use it on a brand new supporter and you will overstate what they are worth. In the example above, running the same nonprofit at a flat 43% instead of 20% then 60% values the donor at $184.81 instead of $154.24, a 19.8% overstatement baked into every bid the algorithm makes on your behalf. That is why this calculator asks for two rates. If your CRM can only give you one, enter it in the first box and leave the second blank, but pulling the two separately is usually an afternoon's work and it changes the answer.
Why the giving season breaks your attribution window
Here is the problem specific to your sector. Roughly 30% of annual giving happens in December, with a meaningful share of that in the last three days of the year. Somebody who subscribes in March may be a genuinely valuable supporter who simply will not give until the appeal lands nine months later.
No Google Ads attribution window sees that. The default conversion window is 30 days and the maximum is 90, so a March signup that becomes a December donor is, as far as the ad platform is concerned, worth nothing at all. This is not a flaw in your tracking. It is the exact reason the signup itself needs a value: you are assigning the value at signup precisely because the gift will arrive long after the platform has stopped looking. If you only report donations as conversions, your spring and summer campaigns will look like failures every year, and the bidding algorithm will learn to stop running them.
The double counting trap
The mirror-image mistake. You value a newsletter signup at $4.63 and mark it a primary conversion. You also track donations as a primary conversion at gift value. Somebody signs up, then gives $50 six weeks later inside the window, and Google counts both. The same money is now in your reported conversion value twice, your return looks better than it is, and the algorithm optimizes toward a number that does not exist.
Two clean ways out. Mark the signup as a secondary conversion so it is reported but not bid on, which is the simplest and is right for many organizations. Or, if signups genuinely lead to giving your tracking never sees (mailed checks, phone gifts, December gifts outside the window, the donor-advised fund gift that arrives with no source at all), keep it primary and value it at only the part your donation conversion never reports. That is the overlap field: enter 50% if your donation tracking already captures about half of what a subscriber eventually gives, and the signup is credited with the rest, here $2.31.
Why this matters more with a Google Ad Grant
If you run the $10,000 a month Ad Grant, conversion values are not a nice-to-have. Grant accounts are capped at a $2 maximum cost per click on manual bidding, which in most competitive auctions means your ads barely appear. That cap is lifted when you use conversion-based Smart Bidding: Maximize Conversions, Maximize Conversion Value, Target CPA, or Target ROAS. Those strategies can only work if conversions are tracked and, for the value-based ones, sensibly valued.
So the chain is short and worth stating plainly: no conversion values, no value-based bidding, no escape from the $2 cap, no competitive placement, and a grant that spends a fraction of its $10,000. Google's guidance for Smart Bidding suggests roughly 15 to 30 conversions in the last 30 days before target-based strategies have enough signal, and many practitioners want to see 30 to 50. For most nonprofits, newsletter signups are the only conversion with that kind of volume. Valuing them properly is what turns them into a usable training signal instead of noise.