Biohacking

Intermittent Fasting Companion

Track your eating and fasting window for 14:10, 16:8, 18:6, or 20:4 protocols, and see your current phase.

Last reviewed: August 2026

Fasting protocol

Time of your last meal today

Result

Fill in the fields to see your result.

How this is calculated

Each protocol restricts eating to a fixed window (10, 8, 6, or 4 hours) and fasts for the remainder of the day. This tool adds your chosen fasting length to your last meal time to mark when your next eating window opens, and compares that to the current time to show your phase.

Choosing a protocol

16:8 is the most studied and most commonly sustainable pattern for most people. Longer windows (18:6, 20:4) are more restrictive and generally better suited to those with prior fasting experience — they haven't shown clearly superior outcomes to 16:8 in most trials, despite being more difficult to maintain.

What the evidence says

Time-restricted eating shows mixed but generally modest effects on weight and metabolic markers in clinical studies, largely comparable to standard calorie restriction. It's one dietary pattern among several, not a guaranteed method, and isn't appropriate for everyone.

Worked example

Example — 16:8 protocol

Last meal finished at 8:00 PM. Adding a 16-hour fast puts the next eating window opening at 12:00 PM the following day. If it's currently 9:00 AM, the tool shows roughly 3 hours remaining in the fasting phase. The 8-hour eating window then runs from 12:00 PM to 8:00 PM.

Common mistakes

Jumping straight to an aggressive protocol. Starting with 20:4 instead of building up from 16:8 tends to increase dropout and can trigger overeating during the short eating window.
Treating the eating window as calorie-unlimited. Time-restricted eating changes when you eat, not automatically how much — total calorie intake still determines weight change over time.
Ignoring hydration and electrolytes during longer fasts. Water, black coffee, and plain tea don't break a fast, but skipping electrolytes during longer protocols can cause headaches or lightheadedness for some people.

Does the fasting window need to include sleep?

Not necessarily, but most people find it easiest to place several fasting hours overnight, since they're asleep for part of it.

Is 16:8 better than 18:6 or 20:4 for weight loss?

Trials generally haven't shown longer windows to produce clearly superior fat-loss results compared to 16:8 — they're simply more restrictive and harder to sustain for most people.

Can I drink coffee during the fasting window?

Black coffee and plain tea (no cream, sugar, or milk) are widely considered compatible with a fast, since they contain negligible calories.

Sources

Patterson RE, Sears DD. "Metabolic Effects of Intermittent Fasting." Annual Review of Nutrition, 2017.
de Cabo R, Mattson MP. "Effects of Intermittent Fasting on Health, Aging, and Disease." New England Journal of Medicine, 2019.

Not medical advice. Intermittent fasting isn't recommended for people who are pregnant, have a history of disordered eating, or manage diabetes with insulin, without medical supervision. Speak with a healthcare provider before starting, especially for longer protocols like 18:6 or 20:4.