Calorie deficit calculator
Enter where you are, where you want to be and the daily deficit you'll run to see the weekly rate, the number of weeks and the date you'd reach the goal.
You'd reach your goal on
17 February 2027
20.0 lb at about 1.00 lb a week from 30 September 2026
How to use it
- Enter your current weight and the weight you're aiming for, in pounds.
- Choose a daily deficit. 500 calories is the standard pound-a-week pace; 250 is gentle; 1,000 is the top of what's usually advised.
- Enter your maintenance calories from the TDEE calculator if you have them, so the calculator can show your daily intake and check it's not too low.
- Read the weekly loss, the weeks and the goal date. Set a start date if you're planning ahead.
Worked example
185 lb now, aiming for 165 lb, a 500 calorie daily deficit, maintenance 2,300 calories, starting today.
20 lb to lose, at 500 × 7 ÷ 3,500 = 1 lb a week. Days: 20 × 3,500 ÷ 500 = 140, which is 20 weeks. Daily intake about 1,800 calories.
At a 750-calorie deficit the same 20 lb takes 94 days, but intake drops to 1,550; at 250 it takes 280 days on 2,050 a day.
How this is calculated
The calculator rests on one rule of thumb: a pound of body fat holds roughly 3,500 calories, so a daily deficit of 500 calories loses about a pound a week and 1,000 loses about two. Weight to lose times 3,500, divided by the daily deficit, gives the days; the goal date is that many days from the start. If you enter your maintenance calories, it also shows what you'd eat each day and warns when that drops below 1,200, the floor most guidelines use for unsupervised dieting. The 3,500-calorie rule is a simplification: as you lose weight your maintenance falls, some early loss is water, and the body adapts, so real progress is usually a little slower than the straight line. Recalculate every ten pounds or so with a fresh maintenance figure.
weight to lose = current weight − goal weight
weekly loss = deficit × 7 ÷ 3,500
days = weight to lose × 3,500 ÷ deficit, rounded up
goal date = start date + days
daily intake = maintenance calories − deficit
Rates, sources and limits
General information for healthy adults, not medical advice. Anyone with a medical condition, who is pregnant, or under 18 should plan weight change with a clinician.
Last reviewed 23 Sep 2026 by the CalcRabbit team. Estimates only, not financial, tax or medical advice.
Frequently asked questions
Is the 3,500-calorie rule accurate?
It's a reasonable average for fat loss over weeks and months, and it's what most planning uses. It isn't exact: early loss includes water and glycogen, your maintenance falls as you get lighter, and the body resists a deficit over time. Expect the real timeline to run 10% to 30% longer than the estimate, and re-run the numbers as you go.
What deficit should I pick?
500 calories a day is the standard recommendation: about a pound a week, sustainable for most people, and rarely low enough to cause trouble. Larger deficits lose faster but are harder to keep up and more likely to cost muscle. Smaller ones are easier and slower. Whatever you pick, the calculator shows the intake it implies; if that's below 1,200 for a woman or 1,500 for a man, pick a smaller deficit or add activity.
Can I create the deficit with exercise instead of eating less?
Yes, and a mix is usually easiest. A 30-minute brisk walk is roughly 150 calories; a run about twice that. Exercise trackers overstate calories burned, so count on somewhat less than they say. The deficit here is the net figure however you produce it.
Where do I get my maintenance calories?
The TDEE calculator on this site estimates them from your height, weight, age and activity level. It's an estimate within about 10%; three or four weeks of tracking your weight against what you eat tells you the real number.