Methodology
Last updated
AllPrayerTime.uk calculates its own prayer times. We do not copy a timetable from another website, and we do not pass a third-party feed through as our own. Every time on this site is produced by our own calculation engine, from the astronomical position of the sun for a specific place on a specific date, under the published settings recorded below.
Because a prayer time is only as trustworthy as the method behind it, this page sets out that method in full: the angles we use, how Asr is derived, what we do with the long UK summer twilight, how times are rounded, the two small margins we add before publishing, and how our results are checked against independent outside sources. Where a choice is ours rather than a settled matter, this page says so.
| Setting | In use on this site |
|---|---|
| Calculation settings | uk-default v1 |
| Calculation method | Muslim World League (MWL) |
| Fajr angle | 18° |
| Isha angle | 17° |
| Asr | Both Standard (Mithl 1) and Hanafi (Mithl 2) — always |
| Long-twilight rule | one-seventh of the night — the night measured from sunset to sunrise |
| Published precision | Nearest whole minute, 24-hour (HH:MM) |
| Calculation engine | AllPrayerTime Engine 1.0.0 |
| Settings in force since | 11 September 2026 |
The calculation method
Fajr and Isha are defined by how far the sun is below the horizon — the twilight angle. We use the Muslim World League convention: Fajr when the centre of the sun is 18° below the horizon, and Isha when it is 17° below it.
Dhuhr is derived from solar transit — the moment the sun crosses the meridian and is at its highest for that day. Sunrise and Maghrib are derived from the sun reaching 0.833° below the horizon, the standard allowance for atmospheric refraction and the width of the sun's disc. Asr is derived from shadow length, described in the next section.
What we can and cannot claim about these angles
Angles follow the Muslim World League convention: 18 degrees for Fajr and 17 degrees for Isha.
Limitation, recorded under OD-2: no primary Muslim World League publication of these angles was located. The 18/17 pairing is attested consistently by praytimes.org, the AlAdhan API and the Adhan library, but not from an original source document.
Limitation, recorded under OD-2: 17 degrees for Isha is a product default, not a UK scholarly consensus. No UK organisation was found endorsing 17 degrees for Isha specifically. Fajr at 18 degrees does have documented UK backing, including the Bradford 1983 and ICC London 1984 conferences and Wifaqul Ulama.
Both Asr times are always calculated, stored and displayed. Neither is presented as the correct one; UK mosque practice is mixed.
High latitudes use the one-seventh-of-the-night rule as a clamp, applied independently to Fajr and to Isha, triggered by actual astronomical conditions rather than by any fixed latitude threshold.
Other calculation conventions in common use set Fajr and Isha at different angles, and UK mosques do not all use the same one. A different angle produces a different time, and neither result is a calculation error. This site publishes one method, states it openly, and does not present it as the only valid one.
Asr: both times, always
Asr is defined by the length of an object's shadow. Two conventions are in wide use, and they differ by roughly an hour in the UK:
- Standard (Mithl 1) — when an object's shadow equals its own length, plus the shadow it cast at midday.
- Hanafi (Mithl 2) — when an object's shadow equals twice its own length, plus the shadow it cast at midday.
We calculate, store and display both. Neither is presented as the correct one, and neither is hidden behind a setting you have to find. UK mosque practice is mixed, and choosing for you would misrepresent that.
Where a single Asr value is unavoidable — a summary line, a page description — we use Hanafi (Mithl 2). That is a presentation default only. It is not a claim that it is the UK standard, and it never changes the address of a page.
Long UK nights and short UK nights
The UK lies far enough north that the twilight angles above cannot always be reached. Around midsummer the sun never sinks 18° below the horizon anywhere in Britain, so there is no angle-based Fajr to calculate at all. On many other dates the angle is reached, but so close to sunrise or sunset that publishing it unadjusted would leave an implausibly short window.
For both situations we use the one-seventh of the night rule. The night — taken for this purpose as the night measured from sunset to sunrise — is divided into seven equal parts. Fajr is not published earlier than the start of the final seventh, and Isha is not published later than the end of the first seventh.
Two different situations, described differently
- The angle was reached, but the limit binds. The angle-based time falls outside the last or first seventh of the night, so the published time is moved to that limit. Both values exist, and the page shows the angle-based time alongside the published one.
- The angle was never reached. There is no angle-based time on that date, so the published time is the one-seventh limit itself, described as an estimate.
Fajr and Isha are handled independently: the rule can apply to one and not the other on the same day. There is no fixed latitude threshold — the rule is triggered by what the sun actually does at that place on that date, not by a line drawn on a map. Every UK location, including the far south-west, loses these angles for part of every year, so a threshold would carry no information.
Where an adjustment has been applied, the prayer times page says so for that specific date and shows the unadjusted astronomical time next to the published one. Nothing is adjusted silently.
Precision and rounding
The engine works in full precision throughout and stores each result as an exact whole number of seconds. Nothing is rounded part-way through the calculation, and no value is ever rounded twice.
Rounding happens once, at the last possible moment, when a time is displayed: to the nearest whole minute, rounding half up. A time falling exactly on the half-second boundary rounds to the later minute. Times are shown as HH:MM in 24-hour format. A value belonging to the following calendar day is labelled as such and is never shown as a bare 00:00.
Rounding is a display rule, not a safety margin. It is kept strictly separate from the publication offsets described next, which are applied at full precision before any rounding takes place.
Publication offsets
Two prayers are published a little after their astronomical instant. These margins are part of the recorded settings, not an adjustment someone can make by hand:
| Prayer | Offset applied before publishing |
|---|---|
| Fajr | None |
| Sunrise | None |
| Dhuhr | 5 minutes later (300 seconds) after solar transit |
| Asr (Mithl 1 and Mithl 2) | None |
| Maghrib | 3 minutes later (180 seconds) after sunset |
| Isha | None |
Dhuhr is published 5 minutes (300 seconds) after solar transit. About a minute of that is definitional — the sun's disc takes 65 to 71 seconds to clear the zenith line — roughly a further minute and a half covers the spread of transit times across a single city, and the remainder is caution. The total aligns with Darul Ifta Birmingham's published plus-or-minus 5 minute istiwa window. This aligns our published start with a documented caution window; it is not a ruling that Zuhr begins at transit plus 5.
Maghrib is published 3 minutes (180 seconds) after sunset. This is a model correction only: refraction variability, terrain and elevation, and the spread of sunset times across a single city — together about 0.4 degrees of horizon depression at London. A further 2 minutes, as used by Wifaqul Ulama, was declined because that portion is discretionary caution attributed to refraction that the measurement does not support.
Fajr, sunrise, both Asr times and Isha carry no offset. The precaution for fasting lives in the 18-degree Fajr angle, not in an added margin, and no separate Imsak time is published.
Sunset itself is never offset. It is the methodology-independent integrity probe used to check the engine against external sources.
Other UK organisations use plus 3, plus 4, or no margin at all. Our published times are shown alongside the unadjusted astronomical instants so the difference is always visible.
What these offsets do not affect
An offset changes the published prayer value only. It never enters any astronomical quantity: not sunrise, solar transit or sunset as we record them, not the length of the night, and not the one-seventh limit described above. Those are always derived from the unadjusted position of the sun, and this separation is enforced by an automated test rather than left to care.
We do not currently publish Islamic midnight, the last third of the night, Ishraq or Tahajjud times. Those definitions are still under review and nothing on this site depends on them.
Imsak and suhoor
We publish no separate Imsak time. It is not calculated, it is not stored as a value anywhere in our data, and it is not displayed. In Ramadan and any other fasting context, Fajr is the time suhoor ends — one value, the whole year round.
Much prayer-time software subtracts a fixed number of minutes from Fajr and labels the result Imsak. We deliberately do not. The caution for fasting already lives in the twilight angle: at 18°, our Fajr is materially earlier than a timetable built on a shallower angle, and subtracting further minutes on top would count the same precaution twice.
Scholars differ on whether a separate Imsak should be observed at all. Publishing no value is the position that takes no side, and it is the safer one: a misread Imsak column could lead someone to pray Fajr before it has begun.
The astronomical calculation
For a given place and date, the engine computes the position of the sun — its declination and the equation of time — using the low-precision solar series published by Jean Meeus in Astronomical Algorithms, the same series behind the NOAA Solar Calculator and the standard basis for prayer-time software. From that position it derives solar transit, sunrise and sunset, and then the hour angles at which the sun reaches each configured twilight angle and each Asr shadow ratio.
Results are carried through in full precision and stored as exact whole seconds. The engine is deterministic: the same place, date and settings always produce the same values, which is what makes an independent check meaningful.
The limits of this calculation
- This is a standard astronomical series, not an observatory-grade ephemeris. Its accuracy is far finer than the minute we publish, but it is not exact to the second.
- It models an ideal, unobstructed horizon. It does not account for your elevation above sea level, hills, buildings or local terrain.
- It uses one set of coordinates for a whole town or city. Sunrise and sunset genuinely differ by up to a couple of minutes across a large urban area.
Calculations on this site are produced by AllPrayerTime Engine 1.0.0. Any change to the engine that would alter a published time requires a new recorded version of these settings; existing times are never quietly recalculated underneath you.
How our times are checked
A calculation that has never been compared with anything outside itself proves nothing. Our generated times are checked against independent external sources, and the results are recorded rather than summarised from memory.
The sources we compare against
- US Naval Observatory (AA Dept) — rise/set/transit — our primary reference for sunrise, solar transit and sunset. It is authoritative, it is independent of every prayer-time library, and it publishes to the minute, which is as fine a comparison as it can support.
- sunrise-sunset.org API v2 — a secondary reference only. It reports to the second and offers an 18° dawn matching our Fajr angle, but its sunrise and sunset carry a consistent difference from every other source we tested, so it is never used as a correctness gate.
- AlAdhan API (MWL, method 3) — our reference for the prayer layer itself, configured to the same Muslim World League angles and the same one-seventh rule we use. It is the only source of the three that produces prayer times rather than solar events.
An important limitation we record openly: the AlAdhan API is derived almost entirely from the praytimes.org libraries, which are also the lineage behind other widely used prayer-time software. It is independent of our engine, but it is one lineage, not two. For the prayer-angle and Asr layers we therefore have a single independent point of comparison, not several, and the US Naval Observatory publishes no Asr time at all.
What counts as agreement
- Sunrise, solar transit and sunset — a difference of up to 60 seconds from the US Naval Observatory. This is the one hard gate: our solar layer has to pass it.
- Fajr and Isha — a difference of up to 120 seconds is flagged for human review. It is a prompt to look, never a block on publishing.
- Asr — review only, never a gate. With a single available point of comparison, treating one implementation's conventions as the truth would be wrong.
- Dhuhr and Maghrib — our own published offsets are subtracted before the comparison is judged. Otherwise our own approved method would register as an error on every single row.
- Rounding — external timetables are published to the minute, so a difference of under 60 seconds can simply be the two sides rounding the same instant differently. That is not a disagreement.
What we have recorded so far
The most recent completed comparison run covered 10 September 2026 to 16 September 2026.
- 210 individual comparisons recorded, covering several UK locations across several dates and all three sources above.
- 45 astronomical comparisons against the US Naval Observatory, of which 0 fell outside the 60-second limit. The largest difference was 36 seconds.
- 8 comparisons flagged for review, which means a human looks at them; it does not mean a time is wrong.
These figures describe agreement with the sources named above under the settings named above. They are not a measure of how closely we match any particular mosque's timetable, and they are not a guarantee of accuracy.
Credits
Solar rise, set and transit reference data from the United States Naval Observatory, Astronomical Applications Department. Prayer-time reference data from the AlAdhan API. Secondary solar reference data from sunrise-sunset.org. None of these organisations endorses this site or its methodology.
Why your mosque may show a different time
If our time and your mosque's time do not match, that does not mean either is wrong. The common reasons are all legitimate:
- A different twilight angle. Fajr and Isha shift by roughly a minute for every tenth of a degree, so a mosque using a different convention will differ by a noticeable margin.
- A different Asr convention. Mithl 1 and Mithl 2 are about an hour apart in the UK.
- Different margins. UK organisations variously add three, four, five or no minutes to Dhuhr and Maghrib.
- A different high-latitude rule, or a fixed timetable agreed locally for the summer months.
- Congregational times are a separate matter. A jamaah time is when a mosque has chosen to gather, which is normally later than the beginning of the prayer window.
For congregational prayer, follow your local mosque. This site is a calculation reference, not a substitute for it. If you believe one of our times is genuinely wrong rather than simply different, please tell us — corrections we accept are published with a reason.
In short
Calculated times — checked against external reference sources. These times are produced by our own calculation engine using the published methodology. Our validation includes astronomical comparison with the US Naval Observatory and prayer-time comparisons against external reference data. Differences can occur between calculation methods, so please follow your local mosque for congregational prayer.