How prayer times are calculated

The five daily prayers of Salah are tied to the sun's path across the sky, not to fixed clock times. That is why the schedule shifts a little every day, differs from one city to the next and jumps when daylight saving time begins or ends. A calculator combines astronomy with a small set of conventions, and knowing those conventions helps you read any timetable with confidence.

AyahFlow, the Quran and Salah app we build at BRUNIQO, includes prayer schedule tools. Like every calculator, it produces estimates based on your settings and your device's location, and it is not a religious authority. The conventions below are general background. For the times you actually pray, your local mosque or community is the reference.

The five prayers and what the calculation looks for

Each prayer time corresponds to an event in the sun's daily movement. Three of them are directly observable; two depend on twilight.

Solar noon rarely matches 12:00 on the clock. It depends on where you are within your time zone, on a small seasonal effect known as the equation of time, and on daylight saving time. In much of the US, solar noon falls closer to 1 p.m. than to noon during the summer months.

Why Fajr and Isha need an angle

At Fajr and Isha the sun itself is below the horizon, so the calculation needs a way to describe how dark the sky is. It does this with the sun's depression angle: how many degrees the sun sits below the horizon. A larger angle means the sun is further down. A Fajr angle of 18 degrees therefore produces an earlier Fajr than an angle of 15 degrees, and an Isha angle of 18 degrees produces a later Isha than 15 degrees.

The angles translate traditional descriptions of dawn and nightfall into astronomical terms, and scholars and organizations have reached different conclusions about which values match those descriptions best. That is the main reason two timetables for the same city can differ by a quarter of an hour or more at Fajr and Isha, while agreeing closely at Dhuhr and Maghrib.

Common calculation conventions

Prayer apps and websites usually offer a list of named conventions. The table shows the parameters commonly published for the best-known ones, as documented by the open-source PrayTimes.org project.

In North America, the Fiqh Council of North America publishes a suggestion of 15 degrees for both Fajr and Isha in the United States and 13 degrees in Canada; the US value matches the ISNA parameters found in many apps. Mosques and communities still make their own choices, and some add a few minutes of caution, known as ihtiyat, to the calculated times. Shia communities that follow the Jafari school also use their own conventions, for example for Maghrib, and publish their own timetables. A name in a settings list is a convention, not a verdict on which practice is right.

The Asr shadow rule

Asr is calculated from shadow length rather than a twilight angle. Under the standard rule, followed in the Shafi, Maliki and Hanbali schools, Asr begins when an object's shadow equals its own height plus the length of its shadow at noon. Under the Hanafi rule, it begins when the shadow equals twice the object's height plus the noon shadow. The Hanafi start is therefore later, and the gap between the two changes with the seasons. Our page on Hanafi and Shafi Asr times explains the difference in detail.

Location, time zone and elevation

Your coordinates determine when the sun rises, peaks and sets for you. Moving east or west shifts every prayer time by about four minutes per degree of longitude, which is why a suburb and a city center can differ by a minute or two. Latitude matters most at Fajr and Isha, because the length of twilight depends on how steeply the sun's path meets the horizon, and that changes with both latitude and season.

Time zones and daylight saving time do not change the sun, only the clock. When the US switches clocks in March and November, every prayer time jumps by an hour on the clock while the astronomical events stay where they were. Elevation has a small effect on sunrise and sunset, because an observer on high ground sees the sun slightly longer; most calculators work with sea-level values for simplicity.

When the formula runs out

In summer, at high northern latitudes, the sun may not sink far enough below the horizon for an 18-degree or even a 15-degree Fajr to occur at all. Calculators then fall back on adjustment rules, such as dividing the night into portions. This affects the northern edge of the contiguous US, all of Alaska and much of Canada around the June solstice. We describe these rules, and why Fajr moves so much through the year, in our article on why Fajr moves through the seasons.

Putting the inputs together

A prayer time is the result of astronomy plus choices. The astronomy is the same for everyone at a given place and date: the sun's position can be calculated very precisely. The choices are human: which twilight convention, which Asr rule, which high-latitude rule, which location and which clock. The table summarizes which input affects which prayer.

When two sources disagree, one of these inputs is almost always different. Our guide on why your prayer times differ from the mosque timetable walks through how to find which one.

Settings, not verdicts

No calculator can tell you which convention your community follows, but your mosque can. That is why AyahFlow shows its prayer schedule as an estimate based on your settings and your device's sensors, and why it says openly that you should verify locally whenever accuracy matters. Use the background on this page to understand what a timetable is doing, and use your local community's timetable to decide when you pray.