semkuBody percentage calculator weight loss
Enter starting and current weight to calculate weight loss percentage.
Goal and dates (optional)
Add your own goal or both dates for additional results.
Enter both dates or leave both blank.
Sources
NIST — SP 811: Guide for the Use of the International System of Units (SI)
SP 811 (2008), p. 53, footnote 22 gives 1 lb = 0.45359237 kg as an exact conversion. This calculator uses that defined value to convert weight displays between lb and kg.
NIDDK — Choosing a Safe & Successful Weight-loss Program
NIDDK says experts recommend an initial weight-loss goal of 5% to 10% of starting weight within 6 months.
This calculator’s 5% and 10% lines are arithmetic comparisons calculated from starting weight; this calculator does not set or recommend goals. NIDDK has not reviewed or endorsed this calculator.
This is not health or weight loss advice and does not assess whether your goal or rate of change is appropriate.
Calculation rules
The starting weight is the denominator of the weight loss percentage; its sign is the opposite of ordinary percentage change.
This calculator uses only starting and current total body weight, so it does not calculate body fat percentage or the amount of fat lost.
The goal is an arithmetic reference you enter yourself, with no automatic recommendation; the 5% and 10% reference weights are arithmetic comparison lines, and this calculator does not set goals.
The period uses the difference in calendar days between your dates, without time-of-day or daylight-saving adjustments; no future goal date is predicted.
Intermediate values are not rounded; percentages, weights and weekly averages are displayed to two decimal places, with ties away from zero, and direction uses unrounded values.
Inputs exist temporarily in your browser; this tool has no saved weight history or tracking graph and puts no inputs or results in the URL or browser storage.
Weight loss percentage = (starting − current weight) ÷ starting weight × 100; goal progress = (starting − current weight) ÷ (starting − goal weight) × 100; average weekly change = (starting − current weight) ÷ (days ÷ 7).
Results are rounded to two decimal places, with ties away from zero; direction and reference-weight comparisons use unrounded values.
Frequently asked questions
- How is weight loss percentage calculated?
- Subtract current weight from starting weight, divide by starting weight and multiply by 100; 80 → 74 kg gives 6 ÷ 80 × 100 = 7.50%.
- What if my weight increases or stays the same?
- An increase gives a negative weight loss percentage: 80 → 82 kg gives −2.50% and a 2.00 kg gain; unchanged weight gives 0.00%.
- What happens if I go past my goal?
- The displayed percentage is not capped: with a starting weight of 80 kg, a goal of 68 kg and current weight of 66 kg, progress is 116.67%; only the bar stops at 100%.
- What does the weekly average mean?
- Weight change is divided by the number of calendar days divided by 7; the example from 2026-08-01 to 2026-09-26 spans 56 days and gives 0.75 kg/week, an observed average rather than a recommended rate.
- Is weight loss percentage body fat percentage?
- No. This is a percentage change in total body weight relative to the starting weight; it does not estimate body fat percentage or the amount of fat lost.
Calorie calculator from macros
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Calculations run in your browser without sending your calculation inputs or results to the server.