Question 1

How many calories deficit do I need to lose 1kg a week?

Accepted Answer

Roughly 1,100 calories per day below your TDEE, since a kilogram of body fat is approximately 7,700 calories, spread across 7 days.

Question 2

What is a safe calorie deficit percentage?

Accepted Answer

A deficit of 10-20% below TDEE is generally considered safe and sustainable for most people, with 20-25% being a more aggressive but still commonly used upper range.

Question 3

How is a calorie deficit calculated?

Accepted Answer

A calorie deficit is calculated by finding your TDEE (total daily energy expenditure) and then eating a set number of calories or percentage below that number.

Question 4

How long will it take to reach my goal weight?

Accepted Answer

Timeline depends on how much weight you want to lose and the size of your deficit — dividing the total calories needed to lose that weight (7,700 per kg) by your daily deficit gives an estimated number of days.

Question 5

Is a 1000 calorie deficit too much?

Accepted Answer

A 1,000 calorie daily deficit can be appropriate for people with a higher TDEE, but for those with lower calorie needs it can push intake dangerously low, so it should be checked against minimum safe calorie thresholds.

Question 6

What is the minimum number of calories I should eat?

Accepted Answer

General guidance suggests not going below about 1,200 calories per day for women or 1,500 for men without medical supervision, regardless of how large your calculated deficit is.

Question 7

Why did my weight loss slow down even though I'm still in a deficit?

Accepted Answer

As you lose weight, your TDEE decreases because a smaller body burns fewer calories, and metabolic adaptation can lower it further, so deficits often need to be recalculated periodically.

Question 8

Should I eat back the calories I burn from exercise?

Accepted Answer

If your TDEE already accounts for your typical activity level, you generally don't need to add back exercise calories separately, though very high-output training days may warrant an adjustment.

Question 9

Is it better to use a percentage deficit or a fixed calorie deficit?

Accepted Answer

A percentage deficit automatically scales with your TDEE and is easier to keep sustainable, while a fixed weekly-loss-rate deficit gives more predictable weight loss timelines — both are valid depending on preference.

Question 10

What happens if my calorie deficit is too aggressive?

Accepted Answer

Very large deficits increase the risk of muscle loss, fatigue, nutrient deficiencies, hormonal disruption, and rebound overeating, making the weight loss harder to sustain long term.

Question 11

Do I need more protein while in a calorie deficit?

Accepted Answer

Yes. Higher protein intake during a deficit helps preserve lean muscle mass, which is why calorie deficit macro splits typically shift toward more protein than a maintenance diet.

Question 12

How often should I recalculate my calorie deficit?

Accepted Answer

Recalculate every 4-6 weeks or after a noticeable weight change, since your TDEE — and therefore your deficit target — shifts as your body weight decreases.

Question 13

Can I take diet breaks during a calorie deficit?

Accepted Answer

Yes. Periodic diet breaks at maintenance calories, every 6-12 weeks, may help reduce metabolic adaptation and improve long-term adherence for some people.

Question 14

Does a calorie deficit calculator account for water weight fluctuations?

Accepted Answer

No. Calorie deficit calculators estimate fat loss based on energy balance, but day-to-day scale weight also reflects water retention, glycogen, and digestive contents, which can obscure the underlying trend.

Question 15

Is 500 calories a day a good deficit for most people?

Accepted Answer

A 500 calorie daily deficit is a commonly used, moderate target that produces roughly 0.45 kg (1 lb) of loss per week for many people, making it a reasonable default starting point.

Question 16

Why is my calculated deficit different from other calculators?

Accepted Answer

Differences usually come from which BMR formula and activity multiplier is used, since small variations in these inputs shift the underlying TDEE that the deficit is calculated from.

Deficit	Typical Weekly Loss	Notes
10% (Mild)	~0.2-0.3 kg	Very sustainable, minimal muscle loss risk
15% (Moderate)	~0.3-0.5 kg	Good balance of speed and sustainability
20% (Aggressive)	~0.5-0.7 kg	Faster results, requires more discipline
25%+ (Very Aggressive)	~0.7-1 kg+	Higher risk of muscle loss and fatigue; short-term use only

Calorie Deficit Calculator (2026)

How a Calorie Deficit Is Calculated

How Long Will It Take to Reach My Goal Weight?

Safe Calorie Deficit Percentage vs Aggressive Deficits

Factors That Affect Your Deficit's Effectiveness

Related Calculators

Scientific References

Calorie Deficit Calculator — Frequently Asked Questions