Weight loss calculator
Losing 5 kg in 10 weeks takes a deficit of about 550 kcal a day, or 3850 a week: enter the target and the week count to plan a cut for a camp or a weigh-in. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Target weight loss
- 5
- Weeks
- 10
- Days
- 70
- Weight unit
- Kg
- Kcal per unit
- 7,700
- Total deficit kcal
- 38,500
Athletes and coaches plan cuts in weeks, not days: an eight-week fight camp, a twelve-week bodybuilding prep, or a six-week return to race weight all start from one arithmetic question — how large a calorie deficit is needed each week, and each day, to lose a chosen amount of weight on time. This weight-loss calculator answers that question with the classic energy-balance constants used in sports nutrition worksheets: about 7700 kilocalories per kilogram of body tissue, or 3500 kilocalories per pound, spread evenly across the weeks you choose. You supply a positive target weight loss and a positive week count; the engine returns the total energy debt, the weekly deficit, and the daily deficit. It does not ask for maintenance calories and it does not invent an intake target, because many training plans already have a fueling strategy and only need the deficit size.
What a weekly weight-loss deficit is and how the numbers are derived
A weekly calorie deficit is the energy gap you must sustain, on average, for seven days so that a chosen amount of body mass is lost by a chosen date. Sports programmes almost always express that horizon in weeks because camps, mesocycles, and fight-week calendars are already week-shaped: an eight-week cut, a twelve-week contest prep, or a four-week return to race weight. This calculator does not estimate your metabolism, does not ask for maintenance calories, and does not invent a daily intake.
It only answers the deficit-size question with the classic energy-balance constants used in coaching worksheets: about 7700 kilocalories per kilogram of body tissue, or 3500 kilocalories per pound. The target weight loss is multiplied by that constant to obtain a total energy debt. Dividing by the week count yields the weekly deficit; dividing that weekly figure by seven yields the daily deficit, which is the same as spreading the total debt evenly across every day of the plan.
Treat the result as a planning estimate, not a medical prescription, and pair it with dedicated BMR or intake tools when you also need a food-log number.
Where a weekly weight-loss calculator earns its keep
Combat athletes, physique competitors, and endurance racers search for a weight-loss calculator because they already know the kilogram or pound figure they must drop and the week count until weigh-in, and they want the weekly and daily calorie gaps those two numbers imply. A publisher ranking for that query is targeting people who plan a cut as a camp, not as an open-ended lifestyle change, and who do not need a maintenance-calorie form in the same step.
Coaches can pre-fill weekly review cards so a fighter dropping five kilograms in ten weeks sees a three-thousand-eight-hundred-fifty-kilocalorie weekly deficit and a five-hundred-fifty-kilocalorie daily deficit without doing the arithmetic between sessions. Classroom and coaching-certification courses that teach the 7700-per-kilogram and 3500-per-pound rules need an oracle that rejects a non-positive target and still returns both daily and weekly figures for valid inputs, because those two cases are how students confuse a formula demonstration with a medical measurement.
Engineers writing fitness-app tests pin known-good pairs so a planning library cannot silently switch from weeks to days, or from kilograms to pounds, without anyone noticing. Failed validation does not consume balance.
What you can do with it
Competition-prep week plans
Turn a kilogram or pound cut goal and a camp length in weeks into a weekly and daily calorie deficit a fighter, lifter, or racer can hold until weigh-in.
FAQ
How does the weight-loss calculator get weekly and daily deficits?
The same identity as spreading the total debt evenly across every day of the plan.
What happens if the target weight loss is zero or negative?
A non-positive loss cannot define a calorie deficit plan and is not billed.
Why does this tool not ask for maintenance calories?
It answers deficit size for a week-shaped cut, not a food-log intake. Supply TDEE from a dedicated calculator if you also need a daily meal target.
Which energy constants are used for kilograms and pounds?
Kilograms use 7700 kilocalories per kilogram. Pounds use 3500 kilocalories per pound.
How many calories a day do I need to cut to lose 5 kg in 10 weeks?
About 550 kilocalories a day. Five kilograms at 7700 kilocalories each is a total of 38500, which spread over 10 weeks is 3850 a week, or 550 a day.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/sports/weight-loss \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"target_weight_loss":5,"weeks":10}'const res = await fetch("https://api.kit.forhosting.com/sports/weight-loss", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"target_weight_loss": 5,
"weeks": 10
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/sports/weight-loss",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"target_weight_loss": 5,
"weeks": 10
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/sports/weight-loss", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"target_weight_loss":5,"weeks":10}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"target_weight_loss":5,"weeks":10}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/sports/weight-loss", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"target_weight_loss": 5,
"weeks": 10
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "sports.weight_loss",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_target_weight_loss | 200 |
max_weeks | 520 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Successful calls cost $0.002; invalid input is not billed.
What a weekly weight-loss deficit is and how the numbers are derived
The response echoes the validated inputs, the kcal-per-unit constant, the total debt, weekly and daily deficits, the equivalent day count, a method tag energy_balance, a short formula string, and the decimal precision used. There is no machine-learning path and no random sampling: either the finite arithmetic succeeds inside the documented limits or the request fails with invalid_input. The product contract is strict on the loss target: zero, negative, missing, or non-finite target_weight_loss is rejected, because a non-positive loss cannot define a calorie deficit plan.
Input contract, units, rounding, and why results stay reproducible
Optional leading plus signs and scientific notation on numeric strings are allowed when they parse as finite decimals; embedded spaces, hex prefixes, and unit suffixes are rejected with a clear message so a bad cell does not become a wrong weekly target. POST a JSON body with two required fields. target_weight_loss is the amount of weight to lose and must be a finite positive number in the unit given by weight_unit; aliases weight_loss, loss, and target_loss are accepted so a form, query string, or spreadsheet export does not need a rename step. Zero, negatives, empty strings, infinities, and non-numeric tokens fail with invalid_input naming target_weight_loss, because a non-positive goal cannot define a deficit. weeks is the plan length and must be a finite positive number; aliases n_weeks, duration_weeks, and timeframe_weeks are accepted so a camp calendar can reuse the same field. Optional weight_unit defaults to kilograms and also accepts kg, kilogram, kilograms, lb, lbs, pound, and pounds; pounds use the 3500 kilocalorie convention while kilograms use 7700. An optional precision field, with aliases decimals and dp, chooses how many decimal places to expose, defaulting to two and capped at fifteen so JSON goldens stay stable. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline; a successful item costs $0.002.
Where a weekly weight-loss calculator earns its keep
Sports-app prototypes can call the same contract from scripts to seed deterministic test vectors for a dashboard that paints weekly_deficit_kcal beside the remaining weeks. This endpoint does not estimate BMR, TDEE, macros, or a safe intake floor; pair it with those dedicated tools when you need them. Keep requests small, pin weekly_deficit_kcal and daily_deficit_kcal in tests, and you get reproducible cut arithmetic for widgets, coaching sheets, and edge workers without standing up a nutrition lab of your own.
Integration use cases
Coaching weekly reviews
Print reproducible weekly_deficit_kcal and daily_deficit_kcal on session cards so a client sees the same numbers the API and the free browser widget produce.
Sports-app test fixtures
Seed CI with the classic 7700/3500 model so a planning library cannot silently switch from weeks to days or from kilograms to pounds.
Technical questions
What does the weight-loss calculator cost?
The browser tool is free. API requests use prepaid balance at $0.002 per successful call; invalid input is not billed.