Weight Loss Calculator
Find daily calorie targets and how long to reach your goal weight — 3 plan options.
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BMI Calculator
Example 1 — Metric
BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.9 — Normal weight
📘 What is the Weight Loss Calculator?
A weight-loss plan is really just a calorie deficit sustained over time, but the size of that deficit determines both how fast you lose weight and how likely you are to stick with the plan. This calculator shows three deficit sizes side by side so you can see the real tradeoff between speed and sustainability before committing to one.
⚙️ How Weight Loss is calculated
TDEE: your starting point
Total Daily Energy Expenditure is calculated from your Basal Metabolic Rate (via the Mifflin-St Jeor equation) multiplied by an activity factor. This is the calorie level at which your weight would stay stable — every plan below is calculated as a deficit from this number.
Why roughly 7,700 kcal equals 1kg of fat
A kilogram of body fat stores approximately 7,700 kilocalories. A 500 kcal/day deficit therefore takes about 15.4 days to lose 1kg in theory — though real-world weight loss is rarely perfectly linear due to water retention and other factors.
The 1,200 kcal safety floor
This calculator never recommends a target below 1,200 kcal/day for women, regardless of how large a deficit the math suggests, since deficits below this floor risk nutrient deficiencies and are difficult to sustain regardless of motivation.
Time to goal
Weeks = weight to lose (kg) ÷ (weekly deficit ÷ 7,700)
500 kcal/day deficit ≈ 0.5 kg/week; 750 kcal/day ≈ 0.75 kg/week
🧮 Worked examples
Example — moderate deficit
Someone needing to lose 8 kg, using a 500 kcal/day deficit.
→ Approximately 16 weeks (about 3.7 months) to reach the goal
Example — aggressive deficit
Same 8 kg goal, using a 750 kcal/day deficit instead.
→ Approximately 11 weeks (about 2.5 months) — faster, but harder to sustain
💡 Original insights & how to use this calculator
Why slower is often genuinely faster
Aggressive deficits are more likely to be abandoned partway through. A moderate, sustainable deficit that you actually complete beats an aggressive one you quit after three weeks — model both timelines here before choosing.
Adjusting as you go
Recalculate your TDEE every 4–5 kg lost, since a lighter body burns fewer calories at rest. Using your starting TDEE for the entire journey causes the plan to become inaccurate partway through.
Pairing with resistance training
A calorie deficit alone does not protect muscle mass. Pairing any of these plans with resistance training and adequate protein (see our Protein Intake Calculator) preserves more lean mass during the loss.
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💡 Expert tips
0.5–1 kg/week is the safe sustainable range.
Never eat below 1200 kcal (women) or 1500 kcal (men).
Add strength training to preserve muscle while losing fat.
📖 Learn more on WellFiLab
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❓ Common questions
How fast can I safely lose weight?
0.5–1 kg per week. Faster usually means losing muscle, not just fat.
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