Case 1
- Sex
- Male
- Age
- 35
- Current weight
- 90kg
- Goal weight
- 80kg
- Height
- 178cm
- Activity level
- Light — PAL 1.375
- Deficit (negative for a surplus)
- 20%
23
Open with these valuesCalorie Deficit Calculator
23weeks
Result: 23 weeksThe result is the number of whole weeks to your goal weight. A deficit set as a percentage of your daily burn shrinks as you lose weight, so progress slows on its own — this recalculates your metabolism day by day instead of dividing a total by a fixed number.
The numbers at a glance
Held fixed: Sex Male, Age 35, Current weight 90.0 kg, Goal weight 80.0 kg, Height 178.0 cm, Activity level Light — PAL 1.375.
| Deficit (negative for a surplus) (%) | Result |
|---|---|
| 5 | 90 |
| 10 | 45 |
| 15 | 30 |
| 20Your value | 23 |
| 25 | 18 |
| 30 | 15 |
Worked examples
Case 2
- Sex
- Female
- Age
- 30
- Current weight
- 75kg
- Goal weight
- 65kg
- Height
- 165cm
- Activity level
- Moderate — PAL 1.55
- Deficit (negative for a surplus)
- 15%
34
Open with these valuesCase 3
- Sex
- Male
- Age
- 25
- Current weight
- 70kg
- Goal weight
- 75kg
- Height
- 180cm
- Activity level
- Moderate — PAL 1.55
- Deficit (negative for a surplus)
- -10%
21
Open with these valuesHow it's calculated
daily: Δkg = TDEE × share / 7700 kcal
- StepEnter your current and goal weight.
- StepAdd age, height and how active your days are.
- StepSet the deficit as a share of your daily burn — enter a negative value to gain.
- ResultRead the number of whole weeks, rounded up.
What this number means
The result is the number of whole weeks a chosen deficit needs to carry you from your current to your goal weight, rounded up. It is arithmetic, not a plan: the field takes anything from −30 % to 30 % and the calculator recommends no value. Each simulated day begins with the daily burn — the Mifflin-St Jeor resting equation for the weight you are at, multiplied by the activity factor. With the preset values, a 35-year-old man of 90 kg and 178 cm at the light factor of 1.375, that burn is about 2533 kcal, so a 20 % deficit is roughly 507 kcal. Divided by the 7700 kcal a kilogram of tissue is taken to hold, that is about 0.066 kg on day one. The weight is then updated and the next day worked out afresh. After 157 days, 23 weeks, 90 kg has reached 80. That is why the projection bends: by the end the burn has fallen to about 2396 kcal and the same 20 % moves only 479 kcal, so the last kilos take longer than the first. Doubling the deficit does not halve the time: 45 weeks at 10 %, 23 at 20 %, 15 at 30 %. The limit that matters most is that 7700 kcal constant — a rule of thumb for fat tissue that overstates loss over long periods, so read a long projection as a direction rather than a date.
Why the projection bends
The deficit is a share of your daily burn, and that burn falls as you get lighter. The calculator recalculates it day by day, which is why the last kilos take longer than the first.
7700 kcal per kilogram is a rule of thumb
The constant describes fat tissue and overstates loss over long periods. It serves here as a conversion, so read a long projection as a direction rather than a date.
The calculator recommends no deficit
The field takes anything from −30 % to 30 % and the arithmetic simply follows it. A larger deficit shortens the projection and nothing else in the calculation changes.
The same arithmetic runs upwards
Enter a goal weight above your current one and a negative percentage to model gaining. Nothing else about the calculation changes.
Commonly misread
Doubling the deficit halves the time.
The relation is not proportional. From 90 kg to 80 kg the calculator gives 45 weeks at 10 % and 23 at 20 %, but 15 at 30 %.
With the deficit held steady I lose the same amount every week.
The deficit is a percentage of a burn that falls as you get lighter. The same percentage therefore moves fewer kilos each week.
The result is the date I will reach my goal weight.
It is a projection from one constant and one metabolic equation, both of them averages. Read it as an order of magnitude, not a calendar entry.
Questions
How long will it take to reach my goal?
The result is the number of whole weeks. From 90 kg to 80 kg at a 20 % deficit the calculator gives 23 weeks; at 10 % it gives 45 and at 30 % it gives 15.
Why does progress slow down on its own?
The deficit is a percentage of your daily burn, and that burn falls as you get lighter. The calculator recalculates it week by week instead of dividing the total by a fixed daily number, which is why the last kilos take longer than the first.
Is the 7700 kcal per kilogram figure exact?
No, it is a rule of thumb for fat tissue and it overstates loss over long periods. It is used here as a conversion, and the falling burn — not the constant — is what makes the projection bend.
How big should the deficit be?
The field takes anything from −30 % to 30 %, and the calculator does not recommend a value. A larger deficit shortens the projection and nothing else in the arithmetic changes.
Can I use it to gain weight?
Yes. Enter a goal weight above your current one and a negative percentage — the same arithmetic then runs upwards.
Sources and last check
Information, not medical advice.