Windows

The best intermittent fasting window is the one you are still doing in March

People search for the window that burns the most fat. The honest answer is that the windows are close, the differences are small, and the only variable that really moves the result is whether you are still doing it in twelve weeks.

By the Steady team · 11 September 2026 · Not medical advice

What the research actually says

Trials that put people on different eating windows and follow them for weeks or months keep finding the same thing. People lose some weight, roughly what you would expect from eating a bit less, and the specific window explains very little of the difference between them. The 16:8 group and the 18:6 group end up close. The early-window group sometimes edges the late-window group, mostly through sleep and not eating in the evening. And in every trial there is a spread within each group far wider than the gap between groups. Some people on 16:8 lose a lot, some lose nothing, and the window did not decide which.

What did decide it was adherence. The people who kept the window kept the result. That sounds obvious and it is, but it is the opposite of how the question usually gets asked. "Which window is best" assumes the window is doing the work. It is not. You are, one decision a day, and the window is a way of making that decision once instead of forty times.

The belly fat question

A lot of people arrive at this page searching for the window that loses belly fat specifically. There is no such window. Where the body takes fat from is set by genetics and hormones, not by how many hours you go without breakfast, and no fasting schedule has been shown to change the order. What fasting can do is help you eat less across the week, and if you lose fat, some of it will come from the middle in the order your body chooses. Anyone selling a window for belly fat is selling the word "belly".

The window is not the mechanism. Eating less over weeks is. The window is just the simplest way to do that without counting.

How to pick a window you will keep

Given that the windows are close, choose on the thing that varies most between them: how they feel on a bad day. Three questions get you there.

1. When is your hard hour?

Everyone who fasts has one. For most it is around hour 12 to 14, when reserves take over and tired, hungry and low tend to arrive together. For some it is a 3pm slump regardless of the clock. For others it is the evening before the fast starts, when the kitchen is right there. Notice which one is yours. Then place the window so the fast ends before that hour, or so the hour lands somewhere busy.

2. What does a normal dinner look like?

Windows that require you to eat dinner at 5pm to hit a number do not survive families, work or friends. Start from a dinner time you can actually keep, count forward, and accept the window that produces. A 15-hour fast you keep beats an 18-hour fast you do twice.

3. Can you do it on a Thursday?

Not on a good Monday with meal prep done. On the day that goes wrong. If the honest answer is no, drop two hours. Nobody has ever failed at fasting because their window was too easy.

Earlier or later

If you can choose freely, an earlier window has a slight edge: finish eating by early evening, and most of the fast happens while you sleep, which is when nobody is hungry. It also tends to improve sleep, which quietly fixes half of the hunger people feel the next afternoon. But this is a small effect. Moving your window earlier by two hours and then dropping the whole thing in week three is a net loss. Put the window where your life is, and if that is a later dinner, that is fine.

What to measure instead of the window

The question "is this window working" usually gets answered with a scale, which moves for a dozen reasons that have nothing to do with fat. Better questions, answerable within two weeks:

• Is the hard hour getting shallower? Not gone, shallower. Most people find it softens over a few weeks as appetite settles.
• Are you finishing more than you cut short? Seven of ten is a schedule that works. Two of ten is a window that needs two hours off it.
• Does the feeling pass? Check in when it is bad and again two hours later. If it usually lifts, you have proof for next time, and next time is easier.

Those three are the numbers Steady keeps, and it keeps nothing else. No weight graph, no water log, no streak. If a window is working, those three say so, and if it is not, they say that too, honestly, with the fasts you ended early counted against it.