Quick answer
Weekly change = (end weight − start weight) ÷ days × 7. Going from 80 kg to 78.6 kg in 28 days is −0.35 kg a week, −0.44% of starting weight per week, with a total change of −1.4 kg.
Enter start and end weights and the days between them. The calculator returns the weekly change and the percentage. Use this weight change rate calculator to check your own figures.
Related tools: Weight Gain Calculator: Daily calorie surplus for a target weekly weight gain. Weight Loss Percentage Calculator: Percentage of starting weight lost.
How to use the Weight Change Rate Calculator
- Choose units: Metric (kg, cm) and Imperial (lb, in).
- Enter starting weight (kg, or lb) (above 0).
- Enter ending weight (above 0).
- Enter days between weights (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Units | Choose one: Metric (kg, cm); Imperial (lb, in) | Starts at Metric (kg, cm) |
| Starting weight (kg, or lb) | A number | > 0 |
| Ending weight | A number | > 0 |
| Days between weights | A number | > 0 |
Formula and method
Formula
rate per week = (end − start) ÷ days × 7
IEEE-754 double precision; shown to the decimals indicated.
Negative values mean weight loss. Informational estimate, not medical advice. Talk to a qualified health professional about your own situation.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Units = Metric (kg, cm); Starting weight (kg, or lb) = 80; Ending weight = 78.6; Days between weights = 28.
| Result | Value |
|---|---|
| Change per week | -0.35 kg |
| Percent of starting weight per week | -0.44% |
| Total change | -1.4 |
Example 2
Inputs: Units = Imperial (lb, in); Starting weight (kg, or lb) = 200; Ending weight = 196.5; Days between weights = 21.
| Result | Value |
|---|---|
| Change per week | -1.17 lb |
| Percent of starting weight per week | -0.58% |
| Total change | -3.5 |
Example 3
Inputs: Units = Metric (kg, cm); Starting weight (kg, or lb) = 60; Ending weight = 61; Days between weights = 14.
| Result | Value |
|---|---|
| Change per week | 0.5 kg |
| Percent of starting weight per week | 0.83% |
| Total change | 1 |
The first line is the headline result (change per week). Below it the weight Change Rate Calculator lists percent of starting weight per week and total change, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Is the rate healthy
Guidance often recommends losing 0.25 to 1 kg (0.5 to 2 lb) a week, or about 0.5 to 1% of body weight. The −0.44% here falls at the gentle end.
Fluctuations
Daily weight swings with water, food and salt, so compare averages over a week or longer rather than single readings. Use the same scale and time of day.
How the result changes with starting weight
Holding every other input at the first worked example, this table changes only starting weight. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Starting weight | Change per week | Percent of starting weight per week | Total change |
|---|---|---|---|
| 40 | 9.65 kg | 24.12% | 38.6 |
| 80 | -0.35 kg | -0.44% | -1.4 |
| 160 | -20.35 kg | -12.72% | -81.4 |
| 320 | -60.35 kg | -18.86% | -241.4 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Starting weight (kg, or lb): entering "0" shows "Starting weight (kg, or lb) must be greater than 0." beside that field and no result.
- Days between weights: entering "0" shows "Days between weights must be greater than 0." beside that field and no result.
Choosing between the Weight Change Rate Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Weight Gain Calculator](/health/weight-gain/) | units and gain per week | Daily calorie surplus |
| [Weight Loss Calculator](/health/weight-loss-calculator/) | units, current weight and goal weight | Days to reach goal |
| [Weight Loss Percentage Calculator](/health/weight-loss-percentage/) | starting weight and current weight | Weight lost |
| [Calorie Deficit Calculator](/health/calorie-deficit-calculator/) | units, weight to lose and time | Daily calorie deficit |
| [Average Rate of Change Calculator](/math/average-rate-of-change-calculator/) | x₁, f and x₂ | Average rate of change |
Background: body measurements and screening
Body-measurement ratios are screening tools, not diagnoses. BMI ignores body composition and fat distribution, and reviews find waist-to-hip and waist-to-height ratios are useful additions but not clearly better than BMI or waist circumference alone. Where the tape goes matters, so measure at the same sites each time.
Some sources quote a waist-to-hip ratio above 0.8 for women and 0.95 for men as a marker of increased metabolic risk; treat that as a screening flag, and talk to a clinician about what your own numbers mean.
Assumptions and limitations
- Day-to-day weight fluctuates with water and food
- Not a diagnosis
This calculator gives general information based on published formulas. It is not medical advice, and it cannot account for your health history. Talk to a qualified clinician about decisions that affect your health.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for starting weight (kg, or lb) and days between weights to confirm this.
Frequently asked questions
How often should I weigh myself?
Weekly or daily with averages.
What is a fast rate?
Over 1% of body weight a week.
Does it work for gain?
Yes, the sign is positive.
What does the Weight Change Rate Calculator calculate?
Average weight change per week and as a share of starting weight. It returns Change per week, Percent of starting weight per week and Total change.
What formula does the Weight Change Rate Calculator use?
rate per week = (end − start) ÷ days × 7. Negative values mean weight loss.
What do I need to enter in the weight Change Rate Calculator?
You enter Units, Starting weight (kg, or lb), Ending weight and Days between weights.
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Day-to-day weight fluctuates with water and food.
What are the limits of this calculator?
Day-to-day weight fluctuates with water and food. Not a diagnosis.
What does the “Units” option change?
It sets how the weight Change Rate is worked out. The choices are Metric (kg, cm) and Imperial (lb, in).
What is an example of a weight Change Rate result?
With units Metric (kg, cm), starting weight (kg, or lb) 80, ending weight 78.6 and days between weights 28, the change per week is -0.35 kg.
Can I rely on this calculator for a decision?
This calculator gives general information based on published formulas. It is not medical advice, and it cannot account for your health history. Talk to a qualified clinician about decisions that affect your health. For this calculator in particular: Day-to-day weight fluctuates with water and food.
Related calculators
- Weight Gain Calculator — Daily calorie surplus for a target weekly weight gain.
- Weight Loss Percentage Calculator — Percentage of starting weight lost.
- Average Rate of Change Calculator — Average rate of change between two points.
- Ideal Weight Calculator — Ideal body weight by four published formulas (Devine, Robinson, Miller, Hamwi).
Sources
- Common definition used on this page. No single authoritative standard defines it, so the exact formula is stated in the formula section above
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.