Ship winners sooner. Kill losers earlier. With a guarantee.

The fastest honest answer an A/B test can give: because every look is statistically valid, Earlycall lets you act at the first trustworthy moment — not at a planned end date, and not on a p-value that quietly breaks the second time you check it.

The speed difference, on a real experiment

A real 13.7M-impression production experiment, hour by hour. Each band is what one method honestly knows; a verdict is safe at the moment its band clears the bar. The ribbon underneath is Earlycall's evidence grade — its answer to "can I trust the data itself right now?"

Earlycall always-valid interval Traditional 95% interval Observed lift

Real production data: ZOZO Open Bandit Dataset (CC BY 4.0, Saito et al. 2020), replayed through the same engine that answers the calculator above. Traditional side: the standard two-proportion z-test on identical inputs.

The rate, not the anecdote

This simulates 20 A/A experiments — no real effect — checked weekly for 12 weeks, the way tests actually get watched. Every "winner" is false, and every false winner is a rollback waiting to happen: the slowest way to ship.

The receipts

We replayed the largest public archive of real A/B tests — 32,487 experiments — through this engine. Of 7,644 declared winners, exactly one was provably better than its runner-up. Read the full analysis →