# BMI Weight Loss Calculator

URL: https://speedycalculator.com/calculators/health/bmi-weight-loss/
Last updated: 2026-10-30

> The BMI weight loss calculator shows the weight you need to reach a target BMI or BMI Prime, how much you need to lose or gain, and how long it would take at a steady weekly rate.

## Inputs

- Weight (kg, lb, st, g)
- Height (cm, in, m, ft, mm)
- Target BMI
- Weekly weight change (kg, lb, st, g)

## Results

- Current BMI
- Current BMI Prime
- Target weight
- Weight to lose (−) or gain (+)
- Target BMI Prime
- Time at your weekly rate

## Formula

```
Target weight = target BMI × height²
Change = target weight − current weight
Weeks = |change| ÷ weekly rate
```

## Explanation

A BMI target turns "lose some weight" into a concrete number. Losing 0.5–1 kg (1–2 lb) a week is the pace most health services recommend, and even a 5% loss improves blood pressure and blood sugar.

### How to use the BMI Weight Loss Calculator

- **Weight**
- **Height**
- **Target BMI**
- **Weekly weight change**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter your weight, height and the BMI you are aiming for. The calculator works out your current BMI, the matching target weight and the difference, and divides the difference by your chosen weekly pace.

### BMI categories

BMI (kg/m²)Category (WHO)BMI PrimeBelow 18.5Underweightbelow 0.7418.5–24.9Healthy weight0.74–0.9925–29.9Overweight1.00–1.1930–34.9Obesity class I1.20–1.3935–39.9Obesity class II1.40–1.5940 and aboveObesity class III1.60 and above

### Inputs explained

FieldWhat to enterWeightUnits: kg, lb, st, gHeightUnits: cm, in, m, ft, mmTarget BMIA numberWeekly weight changeUnits: kg, lb, st, g

### What each result means

- **Current BMI** = [Weight]÷([Height]÷100)^2
- **Current BMI Prime** = [Current BMI]÷25
- **Target weight** = [Target BMI]×([Height]÷100)^2
- **Weight to lose (−) or gain (+)** = [Target weight] - [Weight]
- **Target BMI Prime** = [Target BMI]÷25
- **Time at your weekly rate** = abs([Weight to lose (−) or gain (+)])÷[Weekly weight change]

*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — Weight: 95 kg; Height: 178 cm; Target BMI: 24.9; Weekly weight change: 0.5 kg.

Results — Current BMI = 30; Current BMI Prime = 1.2; **Target weight = 78.9 kg**; Weight to lose (−) or gain (+) = -16.1 kg; Target BMI Prime = 1; Time at your weekly rate = 32 weeks.

## Key terms

- **Target BMI**: The BMI you are aiming for.

## FAQ

**What BMI should I aim for?**
Anywhere from 18.5 to 24.9 is in the healthy range; many people choose the upper end first.

**How fast should I lose weight?**
About 0.5–1 kg (1–2 lb) a week for most adults.

**Does losing weight lower health risk even if I stay overweight?**
Yes – 5–10% weight loss has clear benefits.


## Sources

- [CDC – About BMI](https://www.cdc.gov/bmi/about/index.html)
- [NHS – Lose weight](https://www.nhs.uk/better-health/lose-weight/)