Weight Gain Calculator

Weight Gain Calculator

How many calories do you need to gain weight effectively?

Unit System

About Weight Gain Calculator

This calculator estimates your maintenance calories (TDEE) using Mifflin-St Jeor + activity factor, then adds a controlled daily surplus based on your chosen gain pace. It also estimates the time required to reach your target weight using the common population-level approximation that 1 kg body weight corresponds to about 7,700 kcal.

Formula
Step 1 - BMR (Mifflin-St Jeor):
  Male:   10xW + 6.25xH - 5xA + 5
  Female: 10xW + 6.25xH - 5xA - 161

Step 2 - TDEE = BMR x Activity Factor

Step 3 - Weight Gain Calories = TDEE + Surplus
  Lean gain: +250 kcal/day
  Moderate:  +500 kcal/day
  Aggressive:+750 kcal/day

Step 4 - Timeline estimate:
  Weeks ~= (TargetWeight - CurrentWeight) / [ (Surplus x 7) / 7700 ]
Lean Gain+250 kcal/day
Moderate Gain+500 kcal/day
Aggressive Gain+750 kcal/day
ℹTimeline estimates are approximations. Real-world gain depends on training quality, sleep, food quality, digestion, stress, and adaptive changes in maintenance calories. Recalculate every 2-4 weeks. WHO does not publish a dedicated adult weight-gain equation; this tool uses open energy-balance methods.

Source: Mifflin MD et al., Am J Clin Nutr (1990) · FAO/WHO/UNU Human Energy Requirements (2004) · WHO Healthy Diet Fact Sheet (2024)

Why Structured Weight Gain Matters

Surplus calories are necessary for weight gain, but pace and quality determine whether gains are mostly lean tissue or mostly fat.

01

Uncontrolled Surplus

Large unplanned surpluses increase fat gain disproportionately. A controlled surplus is more effective for body-composition quality.

02

Insufficient Protein & Training

Without progressive resistance training and adequate protein, added calories are less likely to support lean tissue gain.

03

Ignoring Progress Feedback

If body weight is not moving as expected, calories need adjustment. Formula estimates should be refined using 2-4 week trend data.

ℹMedical causes of low body weight should be considered when appropriate. Persistent unintentional weight loss needs clinician assessment.

How to Use This Calculator Most Effectively

Treat this output as a high-quality starting estimate, then personalize with trend-based adjustments:

01

Start with moderate pace if unsure

A +500 kcal/day surplus is a practical default for many people. Move up or down based on weekly weight trend and body composition response.

02

Track weekly averages, not daily noise

Daily body weight fluctuates from hydration, sodium, glycogen, and digestion. Use weekly average changes to judge if your calorie target is working.

03

Prioritize nutrient quality

Use whole-food carbohydrates, sufficient protein, healthy fats, and consistent meal timing. Better food quality improves training performance and recovery.

Frequently Asked Questions