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Calculation Machine

Intermittent Fasting Calculator

Fasting and eating window schedule.

Reviewed by the Calculation Machine team · How we check our maths

Your values

ⓘ Live results

Results
Eating window
12:00 – 20:00
Fast begins
20:00
Fast ends
12:00
Hours fasting
16
Hours eating
8
Fasting hours per week
112

Quick answer

Intermittent fasting sets a daily eating window; 16:8 means 16 hours fasting and an 8 hour window.

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • First meal hour (24h)12
  • Plan16:8

Result

  • Eating window12:00 – 20:00
  • Fast begins20:00
  • Fast ends12:00
  • Hours fasting16
  • Hours eating8
  • Fasting hours per week112

How to use the Intermittent Fasting Calculator

  1. 1Choose the hour of your first meal.
  2. 2Pick a fasting plan.
  3. 3Read your daily eating window.

Frequently asked questions

Does black coffee break a fast?

No — plain coffee, tea and water are fine.

Is 16:8 best?

It is the easiest to sustain; longer fasts offer diminishing returns for most people.

About this calculator

Planning an intermittent fasting window

Intermittent fasting simply schedules when you eat. Popular patterns include 16:8 (a 16-hour fast and an 8-hour eating window), 18:6 and 14:10. The calculator turns your last meal time into the time your fast ends and shows where you are in the window.

Studies generally find intermittent fasting works about as well as ordinary calorie restriction for weight loss. Its main advantage is that some people find a clear eating window easier to stick to.

Making it sustainable

  • Start with 12:12 or 14:10 and lengthen the fast gradually.
  • Water, black coffee and plain tea are generally fine during the fast.
  • Plan protein-rich meals in the eating window so the fast does not cost you muscle.
  • Fasting is not recommended in pregnancy, for people with a history of eating disorders, or for people on glucose-lowering medication without medical advice.

Sources

More questions

Does black coffee break a fast?

It contains almost no calories, so most fasting plans allow it.

Is 16:8 better than eating normally?

For weight loss it performs similarly to other ways of eating fewer calories.