Calorie Deficit Calculator — By Target Date
Enter a goal weight and a date, and this works backwards. Weight to lose × 7,700 kcal, divided by the days available, gives the daily deficit you need. An 85 kg person aiming for 75 kg in 12 weeks needs about 917 kcal a day of deficit — which is aggressive. If the maths lands below 1,200 kcal (women) or 1,500 kcal (men), the date is the problem, not your discipline.
What is Deficit By Date Calculator?
Most deficit tools ask how much you want to lose and hand you a target. This one starts from the deadline, because that is how people actually think — a wedding, a holiday, a medical appointment.
Working backwards exposes unrealistic dates immediately. Losing 10 kg in 6 weeks needs a 1,833 kcal daily deficit, which nobody sustains and which puts most people below a safe intake.
The tool also shows the earliest date that stays above a safe floor, so you can see the gap between what you want and what your body will actually do.
How to use this calculator
- Enter your current weight and the weight you want to reach.
- Enter how many weeks until your target date.
- Add age, height, sex and activity so maintenance can be estimated.
- Read the daily intake — if it is below your safe floor, check the minimum weeks shown.
How the required deficit is calculated▾
Body fat holds roughly 7,700 kcal per kilogram. Weight to lose × 7,700 gives the total deficit needed. Divide by the days until your deadline for the daily deficit, then subtract that from maintenance to get daily intake.
total deficit = weight to lose (kg) × 7,700
daily deficit = total deficit ÷ (weeks × 7)
daily intake = maintenance (TDEE) − daily deficit
min weeks = total deficit ÷ ((TDEE − safe floor) × 7)Source: 7,700 kcal per kg of body fat; Mifflin-St Jeor for maintenance.
Frequently asked questions
Why 7,700 kcal per kilogram?▾
It is the commonly used energy density of body fat. It is an approximation — real loss includes some lean tissue and water, so actual rates vary by 10–20%.
Why does the plan drift after a few weeks?▾
A lighter body burns less. Losing 10 kg lowers maintenance by roughly 200–300 kcal, so the deficit that worked at the start becomes maintenance later. Recalculate every 5 kg.
What if my date is impossible?▾
The tool shows the earliest safe date. Either move the date, reduce the goal, or accept slower loss. Eating below 1,200/1,500 kcal long term costs muscle.
References & method
- 7,700 kcal per kg of body fat; Mifflin-St Jeor for maintenance.
Every formula, its published source and its assumptions are listed on our methodology page. This page is written for information and has not been reviewed by a clinician.
Read the methodology →These figures are estimates from population formulas, not medical advice. Individual needs vary. If you are pregnant, managing a medical condition, or under 18, talk to a doctor before changing your diet.