Qaza calculator
How the calculation works
Prayer becomes an obligation at puberty. A boy reaches it with its physical signs, which can come from the age of 12; a girl with her first period, which can come from the age of 9. If no sign has appeared, the Hanafi school counts a person as adult at 15 — the ruling Qadaar follows, from Kifoya by Sheikh Muhammad Sodiq Muhammad Yusuf.
The calculator takes the day you reached puberty — your date of birth plus that age — and counts every day up to the day you began praying regularly. Each of those days owes one of each prayer: Fajr, Dhuhr, Asr, Maghrib and Isha, and Witr. If you have not started yet, it counts up to today.
If you prayed some of those years, the count is too high; if you missed prayers after you began, it is too low. Treat it as a starting point, and change it in the app as you remember better.
For women: hayd and nifas
A woman does not pray during menstruation (hayd) or the bleeding after childbirth (nifas), and those prayers are not made up — unlike missed fasts, which are. So these days are taken out of the count.
In the Hanafi school hayd lasts at least 3 and at most 10 days, and purity between two periods is at least 15 days. The calculator divides the period into whole cycles of your hayd plus purity days and subtracts the hayd days of each. Nifas is at most 40 days; enter the average for your births. Because cycles change over the years, the result is an approximation.
Witr: Hanafi and Shafiʻi
In the Hanafi school witr is wajib, so a missed witr is made up like the five daily prayers, and the Qadaar app keeps a counter for it. In the Shafiʻi school witr is sunnah and is not owed. Choose Shafiʻi and the calculator leaves witr out.
Making them up
Leaving a prayer without an excuse is a sin that making it up does not wash away on its own — repentance is needed too. If there are too many to know exactly, pray qaza until your heart is content that the debt is paid. To keep it simple, make the intention for the first (or the last) Fajr, Dhuhr and so on that you missed.
Qaza is not prayed at three times: from sunrise until the sun has risen a spear’s length (about half an hour), when the sun is at its zenith, and while it is setting.
This page gives an estimate, not a fatwa. Your situation may have details it cannot see — ask a local imam you trust.