Frequently asked questions
Short answers about the calculators and what the numbers mean.
BMI & body fat
How accurate is BMI?
It's a quick screening tool, not a diagnosis. It can't tell muscle from fat, so very muscular people may read high.
Do BMI ranges differ by ethnicity?
Yes. The WHO suggests lower cut-offs for many Asian populations: overweight from 23 and obese from 25.
Can children use these calculators?
No. Under-18s need age- and sex-specific BMI percentiles, so ask a paediatrician.
BMI or body fat percentage — which is better?
Body fat percentage. BMI uses only height and weight, so it can stay flat while you swap fat for muscle.
What's a healthy body fat percentage?
The fitness range is 14–17% for men and 21–24% for women; average is 18–24% and 25–31%. Going below essential fat (2–5% for men, 10–13% for women) is unsafe.
How accurate is the tape-measure (U.S. Navy) method?
Usually within 3–4% of a DEXA scan, but less accurate for very lean or very heavy bodies. Careful measuring matters most.
Calories, BMR & macros
How many calories do I need a day?
Your BMR multiplied by an activity factor. The Calorie calculator does this and adjusts for your goal.
Why do the BMR and Calorie calculators give different BMRs?
They use different equations (Harris-Benedict and Mifflin-St Jeor). A gap of 50–200 kcal is normal.
Which activity level should I pick?
The one that matches an average week, not your best one. If unsure, pick the lower level.
I'm eating to my target but my weight isn't changing. Now what?
Formulas can be off by 10% or more. Track your weight for 2–3 weeks, then adjust by 100–200 kcal.
Do macros matter more than calories?
No — calories decide whether you gain or lose; macros decide whether that is mostly fat or muscle. Get calories right first.
How much protein do I need?
0.8–1.2 g per kg of body weight for general health, or 1.6–2.2 g per kg if you train hard or are dieting.
Do the macro targets work for keto or vegan diets?
The calorie target does; the default split isn't built for keto. Keep the calories and adjust the split to your diet.
Weight & water
How fast is it safe to lose weight?
About 0.5–1 kg (1–2 lb) a week. Faster loss tends to cost muscle and slow your metabolism.
Is my ideal weight the same as a healthy BMI weight?
No. Ideal-weight formulas give one number; a healthy BMI (18.5–24.9) gives a wider range, which is the better target.
Do tea, coffee and food count toward my water goal?
Yes. All drinks count, food supplies about 20% of your fluid, and normal amounts of caffeine don't dehydrate you.
Can I drink too much water?
Yes — a lot in a short time can dangerously lower blood sodium. Spread your intake through the day.
Using the site
Do I have to re-enter my details on every calculator?
No. What you enter carries across calculators until you close the tab.
Can I use these calculators while pregnant or breastfeeding?
No. Pregnancy changes the numbers, so follow your care provider for weight, calorie and fluid targets.
Formulas for each calculator are under How it's calculated on its page. For anything about your own health, ask a doctor. Still stuck? Contact us.