16/8 Intermittent Fasting Calculator

16/8 is 16 hours of fasting and an 8-hour window for every meal — the most popular schedule and the easiest to start, largely because you sleep through half of it. Enter the time of your last meal below to get your exact hours.

A worked 16/8 day

• Last meal (dinner): 20:00
• Fast ends, 16 hours later: 12:00 the next day — the window opens
• Window closes, 8 hours later: 20:00 — the fast restarts

Move the block wherever it fits. A 10:00-to-18:00 window is the same protocol as a 12:00-to-20:00 one; only the placement changed. Sleep covers about eight of the sixteen fasting hours either way, which is the practical reason this schedule sticks when longer ones do not.

Putting a number on the results

The second-most-searched phrase about this protocol asks how many pounds it is worth. Giving a figure would be dishonest. The result depends on your calorie deficit, and 16/8 does not create one by itself.

The trial that tested this directly is TREAT, cited in the current StatPearls review of dietary approaches to obesity: 16:8 time-restricted eating produced no significantly greater weight loss than unrestricted eating over 12 weeks in adults with overweight or obesity. A separate 12-month trial found calorie restriction plus time-restricted eating did no better than calorie restriction alone.

So the honest framing is that 16/8 is a way of organising when you eat, and any weight change comes from what that organisation does to your total intake. Some people eat noticeably less without tracking anything, because two meals in eight hours is simply less food than three meals plus snacks across fourteen. Others compensate in the window and see nothing move. Work out the target the window has to sit inside with the calorie deficit calculator, and see intermittent fasting for weight loss for the fuller picture.

Eating well inside eight hours

• Lead with protein. It is the macro most likely to fall short when meal count drops, and it is what protects lean mass in a deficit.
• Do not treat the window as compensation for the fast. The total is what decides the result.
• Two or three meals is the usual arrangement; a third smaller meal is often what makes the protein target reachable.

During the fast

Water, plain coffee and unsweetened tea carry no calories and are the standard allowances — they also blunt hunger, which is not a small thing in the last two hours before the window opens.

If 16/8 becomes comfortable and you want a shorter window, the next step is 18/6. Before changing anything, the protocol overview and the contraindications are on the intermittent fasting calculator page.

This content is informational and does not replace evaluation by a physician or dietitian.