FotoBiteCalorie deficit and weight loss time calculator
Enter your current and goal weight and, if you like, how many calories a day you plan to eat. The calculator works out the deficit and a rough timeline, and if the plan is not safe it shows a safe pace instead.
What you enter is not stored or shared: the maths runs in your browser, or on our server without saving anything if JavaScript is off.
Your timeline
Weight to lose: kg.
At kcal a day there is no deficit: you burn about kcal, so your weight will not go down. Below is the timeline at a safe pace.
kcal a day is under the safe minimum of kcal (your basal metabolic rate or kcal, whichever is higher). We do not work out that plan. Below is the timeline at a safe pace.
At kcal a day you would lose about kg a week, faster than 1 kg. We do not show that plan. Below is the timeline at a safe pace.
weeks
weeks
At kcal a day your deficit is kcal, about kg a week.
FotoBite's safe pace: kcal a day, a kcal deficit, about weeks.
This is an estimate. As your weight goes down, so does the energy you burn, so weight loss usually slows towards the end.
A deficit is easier to keep when you can see what you have eaten. Snap your food and FotoBite counts the calories and shows what is left.
Count calories from photos in TelegramNothing from this page is passed to Telegram.
How it was calculated
- Basal metabolic rate about kcal, about kcal a day with activity.
- 1 kg of body weight is taken as a 7700 kcal deficit: weeks = kilograms × 7700 / daily deficit / 7.
We can't give you a timeline
Your basal metabolic rate is about kcal. With these details a safe weight-loss target falls below the minimum of kcal a day, so we don't work out a plan. Double-check height, weight and age; losing weight in this situation is something to do with a doctor.
Not for pregnant or breastfeeding women. If you have an eating disorder or a chronic condition, talk to your doctor first.
This calculator is for adults
FotoBite and this calculation are made for people aged 18 and over. Teenagers need extra energy and protein to grow, so their target is best discussed with a doctor.
Your goal is not below your current weight
This calculator works out weight-loss timelines. To maintain your weight or build muscle, see your target in the calorie calculator.
That goal is below a healthy weight
For your height the lower end of a healthy weight is kg (BMI 18.5). We don't plan weight loss below it.
How the timeline is calculated
- Daily energy use: basal metabolic rate (Mifflin-St Jeor) times an activity factor, as in the calorie calculator.
- Deficit: your daily energy use minus what you eat.
- Timeline: 1 kg of body weight is taken as a 7700 kcal deficit, so weeks = kilograms × 7700 / daily deficit / 7.
Example: a woman, 34, 165 cm, 72 kg, light activity, aiming for 65 kg on 1500 kcal a day. She burns about 1953 kcal, so the deficit is 453 kcal, about 0.4 kg a week. 7 kg × 7700 / 453 / 7 ≈ 17 weeks. FotoBite's safe pace for her is 1453 kcal a day, about 16 weeks.
What pace is safe
The calculator does not show a plan when:
- you would eat less than your basal metabolic rate, or under 1200 kcal a day for women and 1500 kcal for men;
- you would lose more than 1 kg a week;
- the goal weight is below a healthy BMI (18.5).
Instead it shows FotoBite's safe pace: your energy use minus 500 kcal, never below your basal metabolic rate. The app sets its target with the same deficit.
Why the timeline is approximate
7700 kcal per kilogram is an old rule of thumb. As your weight goes down, so does the energy you burn, so weight loss slows towards the end, while the first weeks can be faster because of water. Weigh yourself once a week at the same time and recalculate.
A pace of 0.5–1 kg a week is the NHS recommendation. On weight loss slowing over time: Hall et al., The Lancet (2011).
Frequently asked questions
What calorie deficit do I need to lose weight?
Usually about 500 kcal a day: that is how the FotoBite app sets its target. It is roughly 0.45 kg a week, and the target never drops below your basal metabolic rate.
How long does it take to lose 10 kg?
At a 500 kcal daily deficit, about 22 weeks: 10 × 7700 / 500 / 7 ≈ 22. The real figure depends on how much you burn, so enter your own details.
Why won't the calculator show my plan?
Eating less than your basal metabolic rate, under 1200 kcal (women) or 1500 kcal (men) a day, or losing more than 1 kg a week is not safe. The calculator shows a safe pace instead. Not for pregnant or breastfeeding women. If you have an eating disorder or a chronic condition, talk to your doctor first.
How many calories are in 1 kg of body weight?
Calculations use about 7700 kcal per kilogram. It is an average: part of the weight you lose is water and muscle, not only fat.
Is my data saved?
No. The timeline is worked out in your browser and the numbers you enter are not sent anywhere. With JavaScript off the server does the maths: it stores nothing, and your details never appear in the page address.
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This is a guide, not medical advice. Talk to a doctor before changing your diet. The calculator and FotoBite are for adults, 18+.
Not for pregnant or breastfeeding women. If you have an eating disorder or a chronic condition, talk to your doctor first.