5:2 Diet Calorie Calculator

Two fasting days, five normal days. Enter your stats and see your weekly average, weekly deficit, and the equivalent daily-deficit target — so you can decide which path is easier to live on.

Your Stats

Gender

Your Results

Weekly average calories
—
cal/day averaged across the week
Enter your stats to see your 5:2 numbers.
Your week
Fasting days × 2
—
cal/day on the 2 fasting days
Normal days × 5
—
cal/day on the 5 normal days (maintenance)
Daily-deficit equivalent
—
Estimated fat loss
—/ week

Using 3,500 cal per lb of fat as the standard accounting heuristic. Actual rate varies by adherence — 5:2 has notoriously high day-to-day variance because the fasting days are hard.

The 5:2 protocol, in one paragraph

The 5:2 diet, popularized by Dr. Michael Mosley, asks for two non-consecutive "fast days" per week at 500 calories (women) or 600 calories (men). The other five days you eat at maintenance — no restriction, no tracking, no virtue. The weekly deficit comes from the two hard days. The advertised promise: a real calorie deficit without the day-in-day-out grind of traditional dieting.

The math, made obvious

If your TDEE is 2,200, your week looks like:

  • 2 fasting days × 500 cal = 1,000 cal
  • 5 normal days × 2,200 cal = 11,000 cal
  • Weekly total: 12,000 cal
  • Weekly average: 1,714 cal/day
  • Weekly deficit vs. maintenance: 3,400 cal ≈ 1 lb of fat

That same 1 lb/week could come from eating 1,714 cal every day with no fasting. The math is identical. The experience is not.

The adherence question

On paper, 5:2 looks easy: only two hard days per week. In practice, 500 calories is genuinely brutal for most people who haven't done it before. You're hungry, your sleep gets choppy, and social plans on fasting days become awkward. The Krista Varady research on intermittent fasting consistently finds high dropout rates — much higher than for daily deficits — because the fasting days are the floor of the difficulty distribution, not a smooth curve.

On the other side: some people find fasting days genuinely easier than daily restriction. They'd rather have two miserable days than seven mediocre ones. Personality matters more than metabolism here.

How to actually run 5:2

  • Pick the two days deliberately. Avoid days with hard workouts, social events, or stressful work. Many people like Monday + Thursday (a recovery rhythm) or Tuesday + Friday.
  • Prioritize protein on fasting days.500–600 calories should be ~50% protein. A chicken breast and a salad fits. A muffin and a latte doesn't.
  • Don't binge on normal days.The plan breaks the moment normal days turn into "earned" eating. Maintenance means maintenance.
  • Track for a month before deciding.Most people know by week 4 whether 5:2 is sustainable for them. If you're still dreading every fasting day at week 4, switch to a daily deficit.

5:2 vs. 16:8 vs. daily deficit

Three roads to the same destination. The differences are behavioral, not metabolic.

  • Daily deficit spreads the pain evenly across the week. Predictable. Boring. Works.
  • 16:8compresses each day's eating window but keeps the calorie load similar from day to day. Often the gentlest entry point for people who hate counting. Run the 16:8 numbers.
  • 5:2 moves all the difficulty into two concentrated days. Higher peak pain, lower frequency. Works for some, terrible for others. OMAD is even more extreme.

Frequently asked questions

Why 500 cal for women and 600 for men?

Those are the original numbers in Michael Mosley's 5:2 protocol — they roughly correspond to ~25% of an average maintenance intake for each sex. The split isn't sacred; some practitioners adjust upward for larger bodies. The calculator uses the protocol numbers.

Do the two fasting days have to be back-to-back?

No — most practitioners deliberately space them out (e.g. Monday and Thursday). Back-to-back fasting days are harder behaviorally and don't change the weekly math.

Should I eat under maintenance on normal days too?

The classic protocol says no — five days at maintenance, two days deeply restricted. Some people layer a small deficit onto normal days, but it tends to turn the protocol into a 7-day deficit with extra punishment on fasting days, which defeats the purpose.

How does this compare to a daily deficit?

The weekly fat-loss math is identical if the weekly total calories are equal. The calculator shows you the daily-deficit equivalent so you can pick by lifestyle, not math. People who hate dieting every day often find 5:2 easier; people who can't handle very-low-calorie days often find a flat daily deficit easier.

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