Subscription Payback Period Calculator

Setting it out

Payback period is CAC divided by monthly contribution per subscriber: months = CAC ÷ (ARPU × gross margin).

Using contribution rather than revenue matters, since the cost of serving a subscriber comes out of the same money that is repaying the acquisition.

For a business with annual prepayment the cash payback can be immediate even where the contribution payback is months, and the two should not be confused.

A concrete case

$58 of CAC against $21.75 of monthly contribution: 2.7 months.

The revenue version, $58 ÷ $29, gives 2.0 months and understates the true recovery by a third, because it ignores the cost of delivering the service.

At $58 CAC and 2,000 subscribers acquired over a year, the committed capital at any time is roughly 2.7 months of acquisition spend, about $26,000 at the current rate.

Doubling the acquisition rate doubles that commitment, and the additional funding has to exist before the subscribers it buys generate any cash.

What the number hides

It assumes the subscriber survives the payback period, and with front-loaded churn a meaningful share do not. A business with 12% first-month churn loses roughly an eighth of its acquisitions before month two.

Adjusting for that raises the effective payback materially, and the unadjusted figure is the more commonly quoted one.

Where to go from here

Calculate it net of first-period churn: divide CAC by the contribution actually received per acquired subscriber rather than per surviving one.

Then use it to set the growth rate. Available capital divided by payback period gives the sustainable monthly acquisition spend, which is the constraint that binds before the LTV ratio does.

Annual plans and what they do to the constraint

A subscriber paying annually up front delivers twelve months of revenue on day one, which makes the cash payback immediate regardless of the contribution payback.

That transforms the funding position: a business selling annual plans can grow far faster on the same capital than one selling monthly, because the acquisition spend returns immediately rather than over months.

The trade is the discount typically required to persuade someone to prepay, commonly 15% to 20%, which reduces lifetime value in exchange for cash timing. For a self-funded business that is frequently a good trade, and it is one of the few decisions that directly raises the achievable growth rate rather than the efficiency of it.

Blended payback across plans hides the picture where an annual plan pays back immediately and a monthly one takes months, so calculating it per plan is what makes the mix decision visible.

That figure also determines how much discount an annual plan can justify, since the cash timing benefit is quantifiable rather than a matter of preference.

Including the cost of onboarding and any implementation support in CAC produces a truer payback, since those costs are incurred to acquire the subscriber even where they sit outside the marketing budget.

Modelling it under a pessimistic churn assumption is worth doing before committing to an acquisition budget, since payback lengthens sharply when early retention disappoints.