Fitness guides
FitCalcs' guides explain the numbers behind fitness, body weight and running in plain English, then link you straight to the calculator that does the maths. Each one cites its UK source and stays general: this is information, not medical, dietary or training advice.
How many calories should I eat to lose weight?
Set an honest calorie target from your TDEE, and why a modest deficit beats a crash diet.
BMI vs waist-to-height: which actually matters?
Where BMI is useful, where it misleads, and why the NHS now leans on waist-to-height ratio.
How to predict your race time
Use one recent result to estimate your 5K, 10K, half and marathon, with the maths and the caveats.
How much protein do you really need?
What the UK guideline is, where it falls short for active people, and how to set a sensible target.
Editor, FitCalcs
Oliver Mackman is the named editor of FitCalcs and a director of Best Business Loans Ltd (Companies House 16833937), the company that operates the site. He is accountable for its editorial standards, sourcing and corrections, and requires every result to cite the underlying equation and the named UK source behind it, with health tools carrying the appropriate not-medical-advice caveats.
Last reviewed: 12 June 2026