Fasting length is really daylight length
The fast runs from dawn (the end of suhoor) to sunset (iftar), so its length is essentially the length of daylight plus the pre-dawn twilight. Anything that makes the day longer makes the fast longer. The two big factors are your latitude and the time of year.
How latitude changes the day
Near the equator, day and night stay close to twelve hours each all year round, so fasting length barely changes between seasons. The further you move toward the poles, the more dramatically daylight swings: long days in summer and short days in winter. That is why a fasting day in a northern European city can be several hours longer than one near the equator on the very same date.
The role of the seasons
Because the Islamic (Hijri) calendar is lunar, Ramadan moves about eleven days earlier each year relative to the seasons. Over roughly three decades it drifts through the whole year. So a city's Ramadan fasts are long when Ramadan falls in summer and short when it falls in winter — and the effect is stronger the higher the latitude.
Northern vs. southern hemisphere
The hemispheres are mirror images. When the northern hemisphere has its long summer days around June, the southern hemisphere is in winter with short days — and vice versa around December. SalatWaqt notes, on each city page, when that city's fasts are longest and shortest, based on its latitude.
Very high latitudes: the special case
In far-northern and far-southern regions during summer, twilight can persist all night: the sun never drops far enough below the horizon to mark a clear Fajr or Isha, and in extreme cases it barely sets at all. A literal calculation then produces no valid time. Scholars and calculation bodies handle this with a "high-latitude rule" — for instance, estimating the times by the nearest sensible angle, or by dividing the night into proportional parts. SalatWaqt applies an angle-based rule so these locations still receive workable times.
Practical guidance
If you live at a high latitude and your summer fasts feel extreme, speak to a knowledgeable local scholar: several recognised options exist, such as following the timings of the nearest moderate-latitude city or of Makkah. The goal is a fast that is both valid and sustainable.
A worked comparison
Picture the same day in mid-June across three cities. Near the equator — say Singapore — the fast runs around thirteen to fourteen hours, much as it does at any time of year. In a mid-latitude city such as Cairo it might be about fifteen hours. In a far-northern city such as Stockholm the daylight is so long that a literal fast could approach twenty hours, which is where high-latitude rulings come in. Now shift the same comparison to December and the picture flips for the northern cities: Stockholm's fast becomes one of the shortest, while Singapore's barely changes. The equatorial city is stable; the high-latitude city swings dramatically. That swing is the whole story of fasting by latitude.
Planning for long fasts
When fasts are long, preparation matters more than willpower. A suhoor with slow-release foods — whole grains, protein, fruit and plenty of water — helps you last the day, while heavy, salty or very sugary meals tend to bring on thirst. Pacing activity, resting where possible in the afternoon, and breaking the fast gently at iftar all make a long day easier. SalatWaqt's per-city times let you see exactly how many hours to plan for, today and across the month.
In short
Fasting hours are a product of geography and the calendar, not of any one city being "harder." Understanding the latitude effect explains why your fast differs from a friend's abroad — and why a per-location calculation matters.