Health & Medical Calculators
12 practical tools for everyday health questions
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Adult BMI
Weight relative to height.
Adults 20+. Not suitable for pregnancy. BMI does not distinguish muscle from body fat. Asian adults may have increased risk at BMI 23 and above; discuss your individual risk.
BMR / Resting Calorie Needs
Estimate calories used at rest.
Mifflin–St Jeor estimate for adults. Not a daily food target; excludes activity. Not intended for pregnancy, breastfeeding or critical illness.
Daily Maintenance Calories
Estimate daily energy needs including activity.
Uses resting calories × an approximate activity multiplier. This is a starting estimate, not a weight-loss prescription. Not for pregnancy, breastfeeding or children.
BMI-Based Weight Range
See the weight range corresponding to BMI 18.5–24.9.
Adults 20+, not pregnant. A population reference range, not a personal ideal weight or recommended weight-loss target. Asian risk thresholds can be lower.
Waist-to-Height Ratio
Compare your waist size with your height.
Adult screening guide, particularly when BMI is below 35. Measure midway between the lower ribs and hip bone after breathing out naturally. Not for pregnancy.
Age Calculator
Calculate completed years, months and days.
Uses calendar dates. For 29 February birthdays, 28 February is used as the anniversary in non-leap years.
Pregnancy Due Date
Estimate a due date from your last period.
LMP + 280 days, adjusted for regular cycle length. Ultrasound and clinician dating may be more accurate. Not designed for IVF or irregular cycles.
Pregnancy Weeks & Days
Estimate gestational age on a chosen date.
Days since LMP divided by 7. This is an unadjusted LMP estimate; clinician or ultrasound dating takes priority.
Ovulation & Fertile Window
Estimate dates for a regular menstrual cycle.
Assumes ovulation 14 days before the next period. The actual day varies. The estimated fertile window includes the five preceding days and ovulation day. Do not use this to prevent pregnancy.
Target Exercise Heart Rate
Estimate moderate and vigorous exercise zones.
Based on an age-predicted maximum of 220 − age. Medicines such as beta blockers and heart conditions can alter targets; ask your clinician for a personal exercise range.
HbA1c to Average Glucose
Convert HbA1c percentage to estimated average glucose.
ADAG estimate, not a current glucose reading or insulin-dosing tool. Anaemia, haemoglobin variants, pregnancy, transfusion and some kidney conditions can affect HbA1c.
eGFR Kidney Function
Estimate adult eGFR from serum creatinine.
Race-free 2021 CKD-EPI creatinine formula, age 18+. Less reliable with acute kidney injury, pregnancy or unusual muscle mass. One result cannot diagnose chronic kidney disease; urine albumin and repeat tests matter.
Methods and references
- CDC: adult BMI categories
- NHS: BMI and Asian risk thresholds
- Mifflin–St Jeor resting energy equation (rounded coefficients); activity multipliers are approximate.
- NICE: waist-to-height ratio
- NHS: pregnancy due dates
- NHS: menstrual cycle and variable ovulation timing
- American Heart Association: exercise heart rate estimates
- ADAG study: HbA1c and estimated average glucose
- NIDDK: 2021 CKD-EPI creatinine eGFR equation