Is there a free exam countdown app?

Yes. Exam Countdown is free on the App Store and Google Play, with unlimited exams, colour coding, 400+ subject icons, notes, a reminder before each exam and a free Home Screen widget. No time limit, and no account needed, though creating one is also free and backs your exams up. Premium is optional and adds Calendar View, more widgets, detailed alerts, categories and results tracking.

What you get without paying

Unlimited exams. No cap, no trial period.
Live countdowns to the second on every paper.
A colour and an icon per subject, from over 400 icons.
Notes on any exam: room numbers, what to bring, what to revise.
A reminder the day before each one.
The Next Exam Home Screen widget, which follows whichever paper is closest.
Sharing, so a whole class can follow the same countdown.
A free account, so your exams are backed up and come back on a new phone.

No account is needed to start, though making one is free and worth doing: it backs your exams up so a lost or replaced phone does not take them with it. The free version carries adverts.

What Premium adds

Calendar View, the full widget collection including one that ticks every second, detailed alerts at every interval from a year out to the day before, categories, results tracking, and no adverts.

It starts with a free trial. You can also unlock everything for 24 hours by watching a short video, which is the honest way to find out whether Calendar View is useful to you before deciding.

Is the free version actually usable?

Yes, that is the point of it. A full exam season, colour-coded, with a widget on your Home Screen and a reminder before every paper, costs nothing. Premium is for people who want the season on a calendar and more control over when they get nudged.