Turn a daily calorie deficit into a finish line: total deficit to your goal weight, days required, weekly loss rate, and the 1,200/1,500 kcal safety floors checked.
Free toolNo signupFormula shown
Saved & recent
CHECK ENTRYSAVED
RESULT
—
FORMULA USEDCalorie Deficit Calculator
The 3,500-calorie rule and where it bends
The convention says one pound of body fat stores about 3,500 kcal (7,700 per kilogram), so a 500-kcal daily deficit should remove about a pound a week. It is a fine planning rule, and it is exactly what the math here uses. It is also optimistic: as you lose weight your maintenance calories drop, and metabolism adapts, so later pounds come off slower than the first ones.
From deficit to a finish date
The chain is three steps: (current − goal weight) × 7,700 = total deficit needed; total ÷ daily deficit = days on plan; maintenance − deficit = your daily intake. Pacing tiers mirror clinical practice: under 350 kcal/day is mild, 500–700 standard, up to 1,000 aggressive, and beyond that the risk list (muscle loss, gallstones, rebound) grows fast.
Why the scale disagrees with the spreadsheet
Weight moves in steps, not straight lines: a high-salt dinner can add 2 lb of water overnight, and new training hides fat loss behind glycogen and inflammation. Judge a deficit against a two-week rolling average, not a Tuesday morning. If the trend is flat after three honest weeks, adjust intake by 100–200 kcal.
Worked example
A 90 kg man targeting 80 kg with a 500-kcal deficit and 2,600-kcal maintenance.
Total deficit: 10 kg × 7,700 = 77,000 kcal.
77,000 ÷ 500 = 154 days (≈ 22 weeks) at 0.45 kg (1 lb) per week.
Enter current and goal weight in your usual units.
Pick a daily deficit — 500 kcal is the sustainable default.
Paste your maintenance calories from the TDEE calculator.
Read your intake target, weekly rate, and finish date — and any safety flag.
Frequently asked questions
How many calories does it take to lose 1 kg or 1 lb?
The standard convention is 7,700 kcal per kilogram and 3,500 per pound of fat. Eat 500 kcal under maintenance each day and the arithmetic points to roughly 0.45 kg (1 lb) per week, though real bodies drift from the line over months.
What deficit do I need to lose 1 pound a week?
About 500 kcal per day, since 7 × 500 = 3,500 kcal. Combine food cuts with extra activity if 500 from diet alone feels brutal — the deficit only has to exist, not come from one side.
Is the 1,200/1,500 calorie limit a real rule?
It is a widely used clinical floor, not a law of physics. Below roughly 1,200 kcal for women and 1,500 for men it becomes hard to meet protein and micronutrient needs and defend muscle, so levels under the floor warrant professional supervision.
Why am I not losing weight at the predicted rate?
Usually water and tracking: salt, carbs, cycles, and underestimated portions all blur week-to-week readings. Use a two-week average, and if the trend stays flat for three honest weeks, trim intake by 100–200 kcal.
How big a deficit is too big?
Past about 1,000 kcal/day or 2 lb/week of loss, muscle loss, gallstone risk, and rebound hunger climb sharply — this tool flags that ceiling. Heavier people tolerate steeper deficits better; leaner people should stay toward the mild end.
Do I need to update my deficit as I lose weight?
Yes. A smaller body burns less, so the intake that once produced a 500-kcal deficit drifts toward maintenance. Recalculate your TDEE every 4–5 kg (10 lb) and re-run the plan.