Email List Growth Calculator
How large an email list gets over the months ahead, given what joins each month and what unsubscribes or bounces away — and the size it can never grow past.
A list grows by what joins and shrinks by a percentage of what is already there, so the loss grows with the list while the gain does not.
How the email list growth calculator works
A list grows by what joins and shrinks by a percentage of what is already there, so the loss grows with the list while the gain does not. Sooner or later they balance: the steady state is the monthly sign-ups divided by the monthly loss rate, and no amount of time takes the list past it.
The calculator runs the months one by one, then reports the size at the end, what was added and lost along the way, and that ceiling.
Formula: each month: list = list × (1 − churn) + new sign-ups; ceiling = new sign-ups ÷ churn
Worked examples
| Inputs | Subscribers at the end | Note |
|---|---|---|
| Steady programme | 13,229 subscribers | 2% loss a month, ceiling 25,000 |
| No losses | 16,000 subscribers | plain addition |
| Above the ceiling | 52,465 subscribers | a list bought or inherited, shrinking toward 25,000 |
FAQFrequently asked questions
Why does a list stop growing?
Because losses are a percentage of the list while sign-ups are a fixed number. As the list grows the losses grow with it until they equal the sign-ups; from then on the list holds level. That size is sign-ups divided by the monthly loss rate.
What loss rate should I use?
Add the unsubscribe rate to the share you remove through bounces and list cleaning, both per month. Half a percent to two percent a month is typical for a list mailed regularly; a list that is mailed rarely loses more when it is finally mailed.
How do I raize the ceiling?
Either more sign-ups or a lower loss rate, and halving the loss rate doubles the ceiling just as doubling the sign-ups does. Relevance and frequency drive the unsubscribe rate; sign-up forms and incentives drive the other side.
Does this include people who never open?
Only if you remove them. A subscriber who never opens still counts until a cleaning pass drops them, which is why the cleaning rate is entered separately: it is a choice, and it lowers the ceiling.
Where these figures come from
- Interactive Advertising Bureau — measurement guidelines — the impression and viewability definitions CPM depends on
- US Federal Trade Commission — the US advertizing regulator
Last checked: September 2026. These are standard industry definitions; where platforms disagree, the page says so.