See how much weight you could lose with a daily calorie deficit, how long it would take to reach a goal weight, and what deficit you need for your timeline.
How a calorie deficit works
When you eat fewer calories than your body uses, it makes up the difference from stored energy, mostly body fat. The gap between what you burn (your TDEE) and what you eat is your calorie deficit.
Weekly weight loss ≈ daily deficit × 7 ÷ 3,500 (lb) or ÷ 7,700 (kg)
Worked example
Your maintenance is 2,200 calories and you plan to eat 1,700, a 500-calorie daily deficit. That is 3,500 calories a week, so you could expect to lose about 1 lb a week. Going from 180 lb to 165 lb would take around 15 weeks.
Why weight loss slows down
The 3,500-calorie rule is a useful starting point, but real results usually slow over time. As you lose weight, your body needs fewer calories, so the same intake creates a smaller deficit. Water weight can also hide fat loss for a week or two. Recalculate your TDEE after every 10 lb or so.
A sustainable deficit
- 250 to 500 calories a day is a common, sustainable range for most people.
- Keep protein high and include strength training to protect muscle.
- Combine diet and activity: a 250-calorie cut plus a 250-calorie walk can feel easier than cutting 500 from food alone.
Frequently asked questions
How big a deficit is too big?
Very large deficits are hard to sustain and can cause fatigue and muscle loss. Talk to a professional before going below about 1,200 calories a day (women) or 1,500 (men).
Why did I gain weight one day?
Daily changes are mostly water, salt and food in your system. Look at your weekly average.
Related tools
These calculators give estimates for healthy adults based on published formulas. They are not medical advice. Talk to a doctor or registered dietitian before making major changes to your diet or exercise, especially if you are pregnant, under 18 or have a health condition.