2026-09-08
British Summer Time and Prayer Times: What Changes Twice a Year
On the last Sunday in March, British clocks go forward an hour into British Summer Time. On the last Sunday in October they go back to Greenwich Mean Time. Overnight, every prayer time shifts by a full hour — though the sun has not moved at all. Here is what actually happens.
The sun stays; the clock moves
Prayer times are computed from the sun's position and then converted into local clock time. The clock change affects only that second step. The astronomical instant at which Fajr begins is unchanged; it simply gets a different name. That is why all six times move together and by exactly the same amount.
The missing hour
In March the hour between 1:00 and 2:00 a.m. GMT does not exist on the clock. If a prayer time falls mathematically inside it, there is no clock time for it that day. In practice this can affect Fajr in the far north of Scotland in late March. In October the same hour occurs twice, which is harmless in itself but does confuse apps that cache their results.
The effect you actually notice
The change most people feel is Isha. After the March shift it reads an hour later, and through spring it keeps getting later as the days lengthen — in northern England and Scotland it can approach midnight by June. That is not a method problem and not an error; it is the shifted clock combined with genuinely longer days.
GMT is not the same as UTC in practice
Britain is on GMT in winter and BST — one hour ahead — in summer. A timetable that quietly assumes GMT year-round will be exactly one hour wrong for seven months. This is a genuine and common bug in hand-built spreadsheets and older printed tables. Our pages carry the city's own time zone through the calculation, British Summer Time included.
Why some apps get the changeover wrong
Nearly every clock-change bug comes from caching. An app computes the month's times, stores them, and does not recompute after the shift, so for a day you see the old values. Our monthly table is re-checked in the browser against the city's own time zone, so a stale copy does not sit there unnoticed.
What to check
The morning after each change, compare your app against your mosque's posted times. If they differ by exactly one hour, something has cached. A page reload or an app restart almost always fixes it. If you use a printed annual timetable, confirm that it accounts for the change — not all of them do.