Free tool
How long until a cohort pays you back?
Cost per install tells you almost nothing on its own. This turns it into the number that actually decides whether you can scale: the month a cohort stops costing money and starts making it.
Payback
Month 9
A cohort acquired today covers its acquisition cost in month 9.
- Cost per trial start
- $14.55
- Cost per paying subscriber (CAC)
- $45.45
- Net revenue per subscriber month
- $8.49
- Cumulative net over 24 months
- $67.47
How to read the result
The chain matters more than the final figure. If cost per trial start looks fine but cost per paying subscriber is alarming, your problem is trial-to-paid – a paywall, trial length or activation problem, and no amount of cheaper traffic fixes it.
If cost per trial start is already high, the problem is upstream: creative, targeting, or a mismatch between what the ad promises and what the app opens on.
And if payback lands beyond twelve months, the constraint is your cash, not your marketing. Every additional month of payback is another month of working capital locked up in growth you have already paid for.
Questions people actually ask
- Why does this ignore the free-trial period itself?
- Because a trial produces no revenue, so it shifts every month in the projection by the trial length without changing the shape. Add the trial length to whatever payback month you get here and you have the calendar answer.
- What store commission should I use?
- 30% in year one for most apps, dropping to 15% on subscribers who stay past twelve months, and 15% from the start if you are in the App Store Small Business Program or the Play equivalent. The default here is 15%; raise it if neither applies to you.
- Is monthly churn really constant?
- No, and that is this model's main simplification. Real churn is front-loaded – the first renewal loses far more subscribers than the fifth. Constant churn therefore makes early months slightly pessimistic and later months optimistic. For deciding whether payback lands in month 4 or month 14, it is close enough.
- What payback period should I be aiming for?
- Whatever your cash position tolerates. Venture-funded apps commonly run 9-12 months. A bootstrapped app usually needs under six, because every month of payback is a month of working capital tied up in growth.
- Where do I find these numbers in my own data?
- CPI from the ad platforms, trial start rate and trial-to-paid from your MMP or subscription platform, churn from RevenueCat, Adapty or your own backend. If trial-to-paid is not instrumented, that is the first thing to fix – it is the input this calculation is most sensitive to.
Want us to check these inputs against your actual data?
The free app UA audit covers exactly this: whether the numbers you are using are the numbers your accounts are producing, and where the funnel is losing money.