trial-to-paid conversion

Also called: trial conversion, trial to paid, trial conversion rate, free trial conversion

The share of users who start a free trial and then make a first payment.

Trial-to-paid conversion is the share of free-trial starters who go on to pay:

$\text{trial-to-paid} = \frac{\text{trials that ended in a first payment}}{\text{trials that have ended}}$

The denominator is the part people get wrong. Count only trials that have had time to finish (plus a day or two for the store to process the charge). Trials still running can't have converted yet; if you divide by all trials started in the period, the rate is too low, and it looks lowest for the most recent days, which can pass for a sudden drop. This is right-censoring: group trials by start date and read each group only once it has matured.

What rate to expect depends heavily on the trial type:

Opt-out trials (a payment method is required, and the subscription renews automatically unless cancelled) convert a much larger share of starters, but fewer people start them. This is how app-store subscription trials usually work.
Opt-in trials (no payment method; the user must decide to pay at the end) attract more starters but convert a smaller share.

So compare trial-to-paid only between like trials, and look at the product of the two steps too: paywall view → trial start → paid. A useful early signal on the app stores is auto-renew turned off during the trial: most people who will cancel do it in the first day or two, long before the trial ends. And the first payment isn't the finish line: check refunds and the first renewal before calling a trial change a success.

Example

Halves Plus has a 7-day trial. In the week of September 1–7, 800 users start one. On September 10 Maya asks for the trial-to-paid rate.

Naive: 147 first payments so far ÷ 800 trials started = 18.4%. Alarming.
But on September 10 only trials started September 1–2 have ended and been charged (7 days + 1 day for the charge). There are 350 of them, and they account for all 147 payments: 147 ÷ 350 = 42%.

On September 15 every trial from that week has ended, with 328 first payments: 328 ÷ 800 = 41%. The 18.4% was an artifact of counting trials that couldn't have converted yet. The honest report on September 10 was "42% on the 350 matured trials; the rest of the week is still running".

Common mistakes

Counting trials that haven't ended. Divide only by matured trials, or recent periods will always look worse.
Comparing opt-in and opt-out trials. Their rates differ by design; compare like with like, and check starts × conversion.
Stopping at the first payment. Refunds and cancellations before the first renewal can undo a "better" trial.
Changing trial length and reading it too early. A longer trial delays payments; compare cohorts once both have fully matured.
Mixing plans. Monthly and yearly trials convert differently; a shift in plan mix moves the blended rate.

Learn it in the course

How to calculate ARPU and ARPPU · How to calculate ARPU and ARPPU, conversion to paid and trial-to-paid, and how a change in the paywall trigger mix fakes a better paywall.