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Weight gain calculator: calories and weeks to your goal

A weight gain calculator that sizes daily surplus calories and estimates weeks to goal weight from Mifflin-St Jeor TDEE and your weekly gain pace.

Units
Sex
Activity level

Target body weight, not a medical ideal.

Trained lifters usually want the slow end so extra weight is not mostly fat.

Unexplained weight loss and clinical underweight are medical issues. This calculator is not a treatment plan.

What this tool does

This weight gain calculator estimates your TDEE from height, weight, age, sex, and activity, then sizes a daily calorie surplus to match your chosen weekly kg pace and divides the gap to goal weight by that pace for a week count.

How it works

Pick a goal weight and weekly gain pace (0.1–0.4 kg/week). The tool computes Mifflin-St Jeor TDEE, calculates the daily surplus for that pace (weekly kg × 7,700 ÷ 7), caps the surplus near 20% of TDEE, and reports target calories plus weeks to goal. Imperial users enter goal pounds; math stays metric internally.

Formula and methodology

TDEE = Mifflin-St Jeor BMR × activity factor. Daily surplus = weeklyKg × 7,700 ÷ 7 (≈220 kcal/day at 0.2 kg/week). Target = TDEE + surplus, capped near 20% of TDEE. Weeks ≈ |goal − current weight| ÷ weeklyKg. Pace is clamped to 0.1–0.4 kg/week.

How to interpret the result

The week count is a planning sketch, not a deadline. Early scale jumps from creatine or glycogen are not muscle. If the waist races ahead of the bar, slow the weekly kg. Keep protein in the muscle band (roughly 1.6–2.2 g/kg) throughout, including rest days.

Example

Worked example: 70 kg, 175 cm, age 28, male, moderately active → Mifflin-St Jeor TDEE ≈ 2,650 kcal. Goal 74 kg at 0.2 kg/week needs ~220 kcal/day surplus (0.2 × 7,700 ÷ 7). Target ≈ 2,870 kcal. Four kg to goal ÷ 0.2 = about 20 weeks on paper. Re-run when the weekly average lands near 74 kg, not after one creatine jump.

Common mistakes

  • Copying a goal weight from a heavier friend without matching height or frame.
  • Choosing 0.4 kg/week on a trained lifter — faster gains are mostly fat, not muscle.
  • Leaving current weight stale after you have already gained 3 kg on the scale.
  • Eating the surplus without progressive resistance training and expecting lean mass.

When this estimate may be off

  • You are returning from illness or under-eating; catch-up weight is not this model.
  • Creatine, glycogen, or menstrual-cycle water dominate early scale jumps.
  • Goal weight is a guess with no training plan behind it.
  • TDEE was inflated because activity in the dropdown was theater.

Frequently asked questions

How do I calculate weight gain?

Estimate TDEE (Mifflin-St Jeor × activity), pick a weekly kg pace, and size a daily surplus: weekly kg × 7,700 ÷ 7. This calculator does that math and divides your gap to goal weight by the pace for a week count.

How many calories should I eat to gain weight?

Enough above TDEE to match your weekly pace, capped near 20% surplus. At 0.2 kg/week, that is roughly a 220 kcal/day surplus — but the exact number depends on your TDEE. Pair it with ~1.6–2.2 g/kg protein.

How long will it take to reach my goal weight?

Weeks ≈ |goal − current weight| ÷ weekly kg pace. A 70 kg person heading to 74 kg at 0.2 kg/week is about 20 weeks on paper. Real timelines vary with adherence, holidays, and water shifts.

What is a realistic weekly weight gain goal?

Trained lifters often do well near 0.1–0.25 kg/week so extra weight is not mostly fat. Beginners can gain faster in real life; the form caps pace at 0.4 kg/week as an educational brake.

Is this a calorie calculator to gain weight?

Yes. It is a calorie calculator sized for weight gain: TDEE plus a pace-matched surplus, with a week count to your goal weight. For a simple percent surplus without a goal date, try the calorie surplus calculator.

Can I use pounds instead of kilograms?

Yes. Toggle imperial units and enter goal weight in pounds. Weekly pace is still entered in kg/week on this form — 0.2 kg/week is roughly 0.44 lb/week.

How accurate is this weight gain estimator?

It is a planning estimate, not a guarantee. Mifflin-St Jeor predicts groups better than individuals, the 7,700 kcal/kg rule is a shortcut, and bodies adapt. Use two-week weight averages and re-run when TDEE changes.

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