Weight Loss Calculator

Weight Loss Calculator

How many calories do you need to lose weight safely?

Unit System

About Weight Loss Calculator

This calculator estimates maintenance calories (TDEE) using Mifflin-St Jeor plus activity factor, then subtracts a controlled daily deficit based on your selected loss pace. It estimates timeline 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 Loss Calories = TDEE - Deficit
  Gentle:     -250 kcal/day
  Moderate:   -500 kcal/day
  Aggressive: -750 kcal/day

Step 4 - Timeline estimate:
  Weeks ~= (CurrentWeight - GoalWeight) / [ (Deficit x 7) / 7700 ]
Gentle Loss-250 kcal/day
Moderate Loss-500 kcal/day
Aggressive Loss-750 kcal/day
ℹTimeline estimates are approximations. Real outcomes depend on adherence, activity changes, sleep, medications, stress, and adaptive changes in maintenance calories. WHO does not publish a single adult weight-loss equation; this uses open energy-balance methods.

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

Why Structured Weight Loss Matters

Weight loss should reduce health risk while protecting lean mass and long-term adherence.

01

Excessive Deficit

Very low calories can increase fatigue, hunger, and rebound risk, and may raise lean-mass loss risk if protein and resistance training are inadequate.

02

Ignoring Protein and Training

Calorie restriction without adequate protein and strength training can reduce resting metabolic rate over time by increasing lean tissue loss.

03

Unrealistic Timelines

Aggressive timelines often lead to poor adherence. A steady, moderate pace is usually more sustainable and easier to maintain after goal weight is reached.

ℹFor diabetes, thyroid disease, eating disorders, pregnancy, or chronic illness, use clinician-guided plans rather than generic deficit calculators.

How to Use This Calculator Most Effectively

Use this as a high-quality starting estimate and personalize with trend-based feedback:

01

Start moderate, then adjust

A -500 kcal/day deficit is a practical default for many adults. Adjust up or down every 2-4 weeks based on progress, hunger, and recovery.

02

Track weekly averages

Daily body weight fluctuates from water, sodium, glycogen, and digestion. Use weekly average changes to judge whether your deficit is working.

03

Protect lean mass

Keep protein adequate and continue resistance training during fat-loss phases. This improves body-composition quality and supports metabolic health.

Frequently Asked Questions