If you've ever noticed that different mosque timetables show Asr at different times — sometimes 30 to 90 minutes apart — you've encountered one of the most practically significant differences between the Islamic legal schools (madhabs). Both timings are authentically traced to the Companions of the Prophet ﷺ and both are valid to follow.
The two opinions explained
Shafi'i / Maliki / Hanbali: shadow equals object height
According to the majority of classical scholars (Shafi'i, Maliki, Hanbali schools), Asr begins when the shadow of a vertical object equals its own height, added to the length of its shadow at solar noon. For example: if a 1-metre stick casts a 0.3m shadow at noon, Asr begins when the shadow reaches 1.3 metres. This produces the earlier Asr time seen on most digital prayer time tools.
Hanafi: shadow equals twice the object height
The Hanafi school holds that Asr begins when the shadow equals twice the object's height (plus the noon shadow). Using the same example, Asr begins when the shadow reaches 2.3 metres. In summer in the UK, this can be 60–90 minutes later than the Shafi'i calculation.
Where does the difference come from?
Both opinions trace back to the Companions (Sahabah). Ibn Abbas (RA) and others described Jibril (AS) leading the Prophet ﷺ in prayer twice — once at the beginning of the prayer time and once at the end — and it is the identification of those two times that led to the scholarly difference. Imam Abu Hanifa held that the first Asr Jibril led was Dhuhr, making the 'beginning' of Asr the double-shadow time.
The difference of opinion is a mercy for the ummah.
Which should I follow?
Follow the madhhab of the mosque you pray at, or the madhhab you personally follow. If you are Hanafi (common among South Asian British Muslims), use Hanafi Asr. If you follow any of the other three schools, use the standard/Shafi'i time. Both are Islamically valid.
This site shows the standard (Shafi'i/majority) Asr by default. The calculation method toggle on each city page allows you to switch to the Hanafi school, which adjusts the Asr calculation accordingly.
Practical impact in the UK
The difference is most pronounced in British Summer Time (BST). On a long summer day in London, the gap between Shafi'i Asr (~16:45) and Hanafi Asr (~18:30) can exceed 90 minutes. In winter, the gap narrows to around 20–30 minutes because the Sun never rises very high. This is why it matters more in summer — and why some UK Muslims are caught off guard when they move between mosques of different schools.
Can I pray at both Asr times?
You can pray Asr any time between the beginning of the Asr window (by your school's calculation) and just before Maghrib. So if you follow the Shafi'i opinion, praying Asr at 16:45 is valid. If you follow Hanafi, you should wait until 18:30. Praying at the Shafi'i time while following the Hanafi school would, in the Hanafi view, mean you have prayed before Asr has actually begun — so it is important to be consistent with your madhab.