Why prayer times differ: calculation methods and settings

Before changing an app’s settings, establish whether you are comparing prayer-start times or mosque congregation times. Once that distinction is clear, check how each source obtains its start times. East London Mosque, for example, publishes distinct columns for prayer beginnings and congregational prayers, as well as two Asr starting times. East London Mosque timetable

This guide explains the settings used in Sunni prayer timetables. It does not decide between scholarly positions or provide individual religious rulings.

What a prayer time represents

Prayer times are tied to observable signs. A narration in Sahih Muslim places Fajr between dawn and sunrise and describes Dhuhr in relation to the sun passing the meridian. The same narration describes Maghrib’s period as lasting until twilight disappears. These are time boundaries, rather than fixed hours on a clock. Sahih Muslim 612d

For orientation, the five daily prayers are Fajr before sunrise, Dhuhr after midday, Asr in the afternoon, Maghrib after sunset and Isha at night. Sunrise is a separate timetable entry, not a sixth obligatory prayer. Egypt’s Dar Al-Ifta: daily prayers, Sahih Muslim 612a

A mosque’s jama’ah entry tells you when its congregation is scheduled. Do not substitute that column for the prayer’s beginning when comparing timetables. Conversely, a calculated start time does not tell you when a particular mosque will hold its congregation. Check the mosque’s own published schedule when planning to attend. East London Mosque timetable

Why the clock times change

Solar time and civil time are different. The position of the sun relative to a location’s meridian depends on longitude. Civil clocks, by contrast, give places within the same time zone a shared time. The relationship also varies through the year: the equation of time describes the changing difference between apparent solar time and mean solar time. U.S. Naval Observatory: the equation of time

This is why 12:00 on a clock is not a sufficient definition of local solar noon. For a prayer calculation, the location and date must be specified; for the result to display correctly, the time zone must also match the place being calculated. Adhan’s developer documentation explicitly warns against assuming that the device’s time zone matches the calculation coordinates. U.S. Naval Observatory: the equation of time, Adhan documentation

Fajr and Isha: what the angles mean

A twilight angle measures how far the sun’s centre is below the horizon. Astronomy distinguishes civil twilight at 6 degrees, nautical twilight at 12 degrees and astronomical twilight at 18 degrees. These angles mark the morning beginning and evening end of each astronomical twilight category, not three competing religious definitions. The amount of visible light also depends on atmospheric conditions, cloud and the visibility of the horizon. U.S. Naval Observatory: twilight definitions

Prayer-calculation conventions use selected angles for Fajr and Isha. PrayTimes documents, among others:

• Muslim World League: 18 degrees for Fajr and 17 for Isha.
• ISNA: 15 degrees for both.
• Karachi: 18 degrees for both.

These figures describe the software’s named conventions. They are not a claim that every mosque in a named region uses that preset. PrayTimes calculation documentation

Some methods use an interval instead of an Isha angle. Adhan’s Umm al-Qura preset uses 90 minutes after Maghrib; its documentation tells developers to add 30 minutes during Ramadan. That instruction matters: a method’s name alone does not establish that every implementation handles the Ramadan change automatically. Adhan calculation parameters

Ask which convention your timetable follows, and whether Isha is angle-based or interval-based. Do not choose a number merely because it produces a preferred hour.

Asr: why there can be two start times

The usual software distinction is between a shadow equal to the object’s height plus its noon shadow, and a shadow equal to twice its height plus its noon shadow. The first is associated with the Shafi‘i, Maliki and Hanbali schools; the second is the commonly labelled Hanafi setting. The noon shadow belongs in both calculations. PrayTimes calculation documentation

This is a jurisprudential distinction, not an error to remove by making two screens agree. Darul Ifta Birmingham describes the second-shadow position as the relied-upon Hanafi opinion and advises consistency for someone following it, while noting possible leeway in particular circumstances, such as travel. Darul Ifta Birmingham, fatwa 04027

The software label does not capture every opinion within a school. Darul Iftaa Mahmudiyyah records an earlier-start position within Hanafi scholarship as well as the later-start position. That is another reason not to turn an app’s two settings into a blanket judgement about other worshippers. Darul Iftaa Mahmudiyyah, fatwa 987

If you are unsure which Asr setting applies to your practice, ask your imam or a qualified scholar. Give them the setting names and the timetable you currently follow, rather than asking which app is right.

High latitudes: distinguish late twilight from absent twilight

At high northern latitudes in summer, twilight can persist through the night. The British Board of Scholars & Imams distinguishes this from a different situation: twilight eventually disappears, but Isha begins very late. Its guidance says these situations require separate religious consideration and acknowledges legitimate scholarly disagreement. BBSI guidance on summer Isha

Software can apply additional high-latitude rules. Adhan documents middle-of-the-night and one-seventh-of-the-night limits, as well as a twilight-angle rule that derives a fraction of the night from the selected angle. It separately provides strategies for places where sunrise or sunset cannot be calculated. Adhan calculation parameters

Those software choices do not settle the religious question. AMJA’s guidance discusses estimating twilight proportionally using another location and separately addresses regions where night and day cannot be distinguished in the ordinary way. It also records differing scholarly approaches. AMJA: polar prayer times and fasting

If this affects your location, ask your mosque which seasonal timetable it uses, which dates the adjustment covers and the scholarly basis for it. Do not assume that an adjustment intended for absent twilight automatically applies whenever Isha is inconveniently late. BBSI guidance on summer Isha

Official timetables and calculated presets are different sources

Singapore provides a useful example of a published authority timetable. MUIS supplies an official prayer-times dataset through the government’s data portal, updated following the release of its annual timetable. If you want to check an app against MUIS, compare it with that published source for the same date. MUIS official timetable dataset

A calculator’s named preset is a set of calculation parameters. It is not, by itself, evidence that the displayed numbers were retrieved from an authority’s published timetable. Establish whether a service imports the timetable or calculates its own values before expecting an exact match. This is a source-verification step, not a judgement that all independently calculated times are wrong. Adhan calculation parameters, MUIS official timetable dataset

Check location and daylight saving before changing the method

Start with the selected place and Gregorian date. Adhan requires latitude, longitude and date, and recommends displaying the result using the location’s explicit time-zone identifier, such as Europe/London. This also allows the displayed time to reflect local daylight-saving adjustments. Adhan documentation

A one-hour discrepancy across the schedule is a reason to investigate the clock settings first, not proof that the Fajr angle is wrong. For example, the U.S. Naval Observatory’s daily astronomical service adds one hour when its U.S. daylight-saving option applies. Check whether the timetable and app are both using the same local clock convention. This is a diagnostic suggestion, not a definitive explanation of every one-hour difference. U.S. Naval Observatory: time-zone and daylight-saving settings

Investigate small differences before adding offsets

Prayer software can round results and apply individual minute adjustments. PrayTimes documents rounding up, down or to the nearest minute, alongside per-prayer offsets. A small difference therefore warrants checking these settings before changing the underlying calculation method. PrayTimes user manual

A displayed minute also does not imply an observation accurate to the second. The U.S. Naval Observatory notes that atmospheric refraction, the observer’s height and the local horizon can affect observed sunrise and sunset; routine calculations cannot incorporate every local condition. U.S. Naval Observatory: rise and set definitions

When asking for help, send one comparison with the date, place, source timetable and settings visible. Identify the prayers that differ and by how much. Ask whether the explanation is a calculation convention, Asr rule, seasonal adjustment, rounding or a timetable-specific offset. Keep a record of the answer rather than repeatedly changing settings until one day matches.

The practical aim is a documented choice: know which timetable you follow, which settings reproduce its method, and when local scholarly guidance is needed.

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Related reading: When does the daily fast begin and end? · Fasting in Islam: obligations, exemptions and missed fasts. Choose your location and method.