The arithmetic, with your numbers in it
Change any field and the results update as you type. Nothing is sent anywhere; the whole thing runs in the page.
Total, across every tier.
On this site: founder price or needs-it-now. If your form has one tier, this is 100 and the result will flatter you.
The single most sensitive number here. Halving it halves everything below.
For small flat-rate tools, somewhere between 10 and 20 is the honest range. Nobody knows theirs before launch.
- Accounts that actually pay
- 6
- Total revenue from this list
- $3,276
- Worth of one signup, any tier
- $65.52
Divide by every signup, not just the paying ones. This is the number worth carrying around.
At the defaults — 50 signups, 30% on a committed tier, 40% of those converting, $39 a month, 14 months of retention — 6 accounts pay, the list is worth $3,276 in total, and each name on it was worth $65.52.
Assumptions behind these numbers
- Flat monthly pricing with no annual discount and no expansion revenue. Both would raise the result and neither is knowable before launch.
- No churn curve. Retention is modelled as a flat number of months, which overstates early revenue and understates the tail.
- Signups outside the committed tiers convert at zero. That is wrong — some of them buy — but it keeps the estimate conservative and the arithmetic legible.
- Nothing here accounts for the cost of building or running the product, which is the number that decides whether the revenue matters.
Read the number honestly
Sixty-five dollars a signup sounds like a lot until you notice what it is not. It is not sixty-five dollars today; it is sixty-five dollars spread across fourteen months, contingent on a product existing, arriving before the person forgets, and doing the thing they signed up for. Most of that is spending in the future against revenue in the further future.
The number is still useful, for a narrow purpose. It tells you what you can justify spending to get one more signup, and it tells you whether the whole exercise can possibly clear a bar you care about. Fifty signups at sixty-five dollars is about three thousand dollars of eventual revenue. If your idea needs a year of full-time work, three thousand dollars is not a result — it is a polite no with arithmetic attached, and finding that out in an afternoon is the point.
The middle input is where the honesty happens. Twenty percent versus sixty percent changes the answer by a factor of three, and nobody knows theirs before launch. If your decision flips between those two, you have not learned anything from the calculator; you have learned that the decision depends on something you cannot yet measure, which is itself worth knowing before you start building.
What the same list is worth at three different conversion rates
Fifty signups, thirty percent committed, $39 a month, fourteen months. Only the conversion assumption changes.
| Conversion of committed tier | Accounts paying | Total revenue | Per signup | What it would justify |
|---|---|---|---|---|
| 20% — pessimistic | 3 | $1,638 | $32.76 | A weekend, not a quarter |
| 40% — the default here | 6 | $3,276 | $65.52 | A few weeks of evenings |
| 60% — optimistic | 9 | $4,914 | $98.28 | Still not a salary |
Source: Calculated from the formula above at the stated inputs. The three conversion rates are the options offered in the calculator, not observed data.
The right-hand column is the only one that matters, and none of the three rows says "quit your job". That is the normal result for fifty signups and it is why the composition of the list matters more than its length.
Two things wrong with this calculator
Both are real. Neither is fixable with more inputs.
- It assumes the people who did not pick a committed tier are worth nothing.
- It does, and that is false. Some notify-tier signups buy, particularly if the product arrives quickly and does exactly what the page promised. The assumption is deliberately conservative because the alternative is inventing a second conversion rate you have even less basis for. If you want the optimistic version, raise the committed share instead — the arithmetic is the same and the guess is at least visible.
- Flat retention is not how churn works.
- Correct. Real retention is a curve with a cliff in the first two months and a long tail after. Modelling it properly needs a cohort you do not have. Fourteen flat months is roughly what a curve with heavy early churn and a stable remainder averages out to for small flat-rate tools, and it is honest about being a stand-in rather than a measurement.
- None of this survives contact with a product that takes a year to build.
- That is not an objection to the calculator, it is the calculator working. A list decays; a signup from fourteen months ago is closer to a stranger than to a customer. If the build time is long, lower the conversion rate rather than telling yourself the list will keep.