BMI Calculator for Weight Loss

Q: What BMI should I aim for when losing weight?

The WHO healthy range is 18.5–24.9. For weight loss goals, aim for the top of the healthy range first (BMI 24.9) rather than an arbitrary number. Research on long-term health outcomes generally shows the lowest risk in the 22–24 BMI range for most adults. Avoid targeting the lower end of healthy (18.5–20) unless recommended by a clinician, as very low BMI is associated with its own health risks.

Q: Is BMI accurate for tracking weight loss?

BMI is a useful starting point but a poor sole metric for tracking progress. It cannot distinguish fat from muscle — someone gaining muscle while losing fat may see their BMI stay flat or rise while their body composition improves. Supplement BMI with waist circumference (target below half your height in centimetres) and, where accessible, body fat percentage. Track weight as a 7-day rolling average to filter out daily fluctuations.

Q: How long to reach a healthy BMI?

It depends on how much weight you need to lose and your deficit size. Example: a person 172 cm tall weighing 82 kg (BMI 27.7) targeting BMI 23.0 (68 kg) needs to lose 14 kg. At a 500 kcal/day deficit (roughly 0.5 kg/week) that takes approximately 28–30 weeks. Use the BMI calculator to find your target weight, then divide the kilograms to lose by 0.5 to estimate weeks at a moderate deficit.

Q: Does BMI differ by sex, age, or ethnicity?

The standard BMI scale was developed on predominantly European populations and has known limitations. People of South, East, and Southeast Asian descent tend to carry metabolic risk at lower BMI values — some health bodies recommend an overweight threshold of 23.0 and obesity threshold of 27.5 for these groups. Older adults naturally lose muscle mass, so a slightly higher BMI (22–27) is sometimes considered acceptable after age 65. These are population-level adjustments; individual clinical assessment matters most.

BMI tells you whether your current weight is in a healthy range and gives you a concrete target weight to aim for. Here is how to use it to set a realistic goal — and what to track alongside it.

Written and maintained by Russ Rogers, founder and creator of yootils. Last reviewed 22 August 2026.

What BMI Tells You About Weight Loss Goals

Body Mass Index (BMI) converts your height and weight into a single number that maps to population-level health risk categories. For weight loss, it serves two practical purposes: telling you whether you need to lose weight at all, and giving you a concrete target weight to aim for.

The target weight formula is straightforward: target weight (kg) = target BMI × height (m)². If you are 170 cm tall and want to reach BMI 24, your target is 24 × (1.70 × 1.70) = 24 × 2.89 = 69.4 kg. This turns an abstract goal ("I want to be healthier") into a specific, trackable number.

BMI Categories and What They Mean for Weight Loss

BMI	Category	Weight loss action
Below 18.5	Underweight	Weight loss not recommended
18.5–24.9	Healthy weight	Maintain current weight
25.0–29.9	Overweight	Target 0.25–0.5 kg/week loss
30.0–34.9	Obese (Class I)	Target 0.5 kg/week; medical review if no progress
35.0 and above	Obese (Class II+)	Medical supervision recommended

For most adults, an initial target of BMI 24–25 (the top of the healthy range) is more achievable and sustainable than targeting a specific low number. Research on longevity and health outcomes consistently places the lowest risk in the 22–24 BMI range for most adults.

Calculating Your Target Weight from a BMI Goal

Worked example: height 172 cm (1.72 m), current weight 82 kg

Current BMI: 82 ÷ (1.72 × 1.72) = 82 ÷ 2.96 = 27.7 (Overweight)

Step 1 — Set target BMI: 23.0 (mid-range healthy)

Step 2 — Target weight: 23.0 × 2.96 = 68 kg

Step 3 — Weight to lose: 82 − 68 = 14 kg

At a 500 kcal/day deficit (~0.5 kg/week): 14 ÷ 0.5 = 28 weeks

Estimated Timeline to a Healthy BMI

Use this table as a planning guide based on how much weight you need to lose. Times assume a consistent 500 kcal/day deficit (moderate, sustainable) or a 250 kcal/day deficit (slow, conservative).

Weight to lose	At 0.25 kg/week	At 0.5 kg/week
5 kg	20 weeks	10 weeks
10 kg	40 weeks	20 weeks
14 kg	56 weeks	28 weeks
20 kg	80 weeks	40 weeks

These are estimates based on 7,700 kcal per kg of fat. Actual rate varies with individual metabolism, body composition changes over time, and dietary adherence. Recalculate your BMR-based deficit every 4–6 weeks as your weight changes.

BMI Limitations for Weight Loss Tracking

Muscle vs fat: BMI cannot distinguish between lean tissue and fat mass. Someone doing resistance training while losing fat may see their BMI plateau or barely move, while their body composition improves significantly. If this applies to you, supplement BMI tracking with waist-to-height ratio (WHtR) — a waist circumference below half your height in centimetres is the target, and it tracks visceral fat more accurately than BMI alone.

Ethnicity: The standard WHO BMI thresholds were developed on predominantly European populations. South, East, and Southeast Asian adults carry metabolic risk at lower BMI values — the WHO Asia-Pacific guidelines recommend an overweight threshold of 23.0 and an obesity threshold of 27.5 for these groups. If this applies to you, set your target BMI accordingly.

Daily fluctuations: Body weight varies by 1–2 kg from day to day due to water retention, gut contents, and hydration. Weigh yourself at the same time each day (morning, after the bathroom, before eating) and track a 7-day rolling average rather than reacting to individual readings. Consistency of measurement matters more than the precise number on any given day.

What to Track Alongside BMI

Waist circumference: target below height (cm) ÷ 2. More sensitive to visceral fat loss than BMI
Body fat percentage: if accessible via DEXA, bioimpedance, or skinfold — see the body fat calculator
Energy levels and sleep quality: subjective but important signals that your deficit is not too aggressive
Clothing fit: practical proxy that does not require a scale
Strength metrics: if doing resistance training, maintaining or increasing lifts is a strong signal that muscle is being preserved

Enter your height and weight into the yootils BMI calculator to get your current BMI, weight category, and healthy weight range instantly.

Open BMI Calculator →

Also see: Body Fat Calculator · Healthy Weight Calculator

Frequently Asked Questions

What BMI should I aim for when losing weight?

Aim for the top of the healthy range first — BMI 24.9. Research places lowest long-term health risk in the 22–24 range for most adults. Avoid targeting the lower end (18.5–20) unless clinically advised, as very low BMI carries its own risks.

Is BMI accurate for tracking weight loss?

Useful as a starting point, but it cannot distinguish fat from muscle. Supplement with waist circumference (target below height÷2 in cm) and body fat percentage. Track weight as a 7-day rolling average to filter out daily fluctuations.

How long to reach a healthy BMI?

Example: 172 cm, 82 kg (BMI 27.7) targeting 68 kg (BMI 23.0) = 14 kg to lose. At 500 kcal/day deficit (~0.5 kg/week): approximately 28 weeks. Divide kg to lose by 0.5 to estimate weeks at a moderate deficit.

Does BMI differ by sex, age, or ethnicity?

Yes. South, East, and Southeast Asian adults carry risk at lower BMI — WHO Asia-Pacific guidelines suggest 23.0 as the overweight threshold. After age 65, a slightly higher BMI (22–27) is sometimes acceptable. Individual clinical assessment matters most.

Evidence & Methodology

How This Page Is Grounded

Method

Uses the BMI equation to translate a selected target BMI into a corresponding weight at the entered height.

Important limitation: A BMI-derived target is a screening reference and does not account for body composition or personal clinical needs.

Primary Sources

Obesity and overweight World Health Organization
Calculate your body mass index NHS

Quality Checks

Target-weight examples and unit conversions are checked against the BMI calculator.

Published by: yootils
Source authority: World Health Organization, NHS
Last reviewed: 22 August 2026

See how sources are selected and corrections are handled in our Editorial & Calculation Methodology, and which automated checks this page has to pass in How We Test.