Why track bmi calculator in ClinicalTools
Body mass index is a blunt instrument, but it is still the number your doctor, your insurer and most clinical guidelines start from. ClinicalTools makes it painless to calculate correctly, in feet and inches or centimetres and kilograms, and — more usefully — to keep a history so you can see direction rather than a single reading.
Along with the BMI value the app shows your category (Underweight, Normal, Overweight or Obese) and the weight range that would put you in the normal band for your height. If you enter an age of 65 or older, the category cut-offs shift to the slightly higher thresholds often used for older adults.
Each calculation you save is added to a history chart and, if you allow it, written to Apple Health as both a BMI and a body-weight sample. For a better picture of central fat, pair it with the Waist-to-Height Ratio calculator.
Three steps, every time.
Enter height and weight
Use feet/inches and pounds, or centimetres and kilograms. Optionally add your age for senior-adjusted thresholds.
Read the result
See your BMI, its category on a colour scale, and the healthy weight range for your height.
Save and track
Save the calculation to your history and chart. The value is also written to Apple Health.
What the BMI Calculator tool does
Category and healthy range
Underweight, Normal, Overweight or Obese, plus the weight range that corresponds to a BMI of 18.5–24.9 at your height.
Thresholds for adults 65+
Enter an age of 65 or above and the normal band shifts to roughly 22–27, reflecting the thresholds commonly used for older adults.
History chart
Every saved calculation is plotted over time, so you can see a slow drift or a steady improvement.
Imperial and metric
Switch units freely; conversions are exact and the stored history stays consistent.
Apple Health
Each saved calculation writes BMI and weight to Apple Health, keeping the Health app and any connected apps up to date.
PDF export
Export your BMI history as a PDF or include it in the combined Doctor Share report.
BMI categories used by the app
Standard adult thresholds. With an age of 65+ entered, the normal band becomes 22.0–26.9.
| Category | BMI (adults) | BMI (65 and older) |
|---|---|---|
| Underweight | Below 18.5 | Below 22.0 |
| Normal | 18.5 – 24.9 | 22.0 – 26.9 |
| Overweight | 25.0 – 29.9 | 27.0 – 29.9 |
| Obese | 30.0 and above | 30.0 and above |
BMI does not distinguish muscle from fat and does not account for where fat is carried. Use it alongside waist measurements and your clinician's advice.
Source: CDC — Adult BMI Categories
For weight goals, check-ups and insurance forms
Anyone working toward a weight target uses the history chart to see progress without obsessing over daily scale noise. People preparing for a physical or filling in an insurance questionnaire get an accurate, dated value. Older adults get category thresholds that better reflect their age group.
Your bmi calculator data stays yours.
No account, no login, no server run by us. Data lives on your iPhone or iPad and, if you turn on iCloud sync, in your own end-to-end-encrypted iCloud account. Every export and share is something you start.
BMI Calculator — common questions
Is the BMI calculator free?
Yes. BMI Calculator, its history chart, Apple Health writing and PDF export are all free.
Why does my category change when I enter my age?
For adults aged 65 and older the app uses slightly higher thresholds (normal 22–27) that are commonly applied to older adults, where a little extra weight is associated with better outcomes.
Is BMI accurate for athletes?
BMI can overstate risk for very muscular people because it cannot tell muscle from fat. The Waist-to-Height Ratio tool in ClinicalTools is a useful complement because it looks at central fat directly.
Does it write to Apple Health?
Yes. When you save a calculation, the BMI and the weight you entered are written to Apple Health (with your permission).
Can I switch between pounds and kilograms?
Yes, at any time. History is stored in metric and displayed in whichever unit you choose.