Science-Backed Tools

Fasting Calculators

Four free tools built around the science of intermittent fasting. Calculate, plan, and understand your body — no sign-up required.

4 tools in one
Fasting Calculator

Plan your eating window, calculate your TDEE and calorie targets using Mifflin-St Jeor, track your metabolic fasting stage, and plan a 5:2 or ADF week.

Fasting window & eating schedule
BMR, TDEE & calorie targets
Metabolic stage tracker
5:2 & ADF weekly planner
Open calculator
Body composition
BMI Calculator

Calculate your Body Mass Index and get fasting protocol recommendations tailored to your BMI category — including what to watch for and where to start safely.

Metric & imperial support
Healthy weight range for your height
Fasting protocol by BMI category
Category-specific safety guidance
Open calculator
Hydration
Water Intake Calculator

Find out exactly how much water you need based on your weight, activity level, climate, and whether you are currently fasting — when hydration matters most.

Personalised daily water target
Fasting-adjusted hydration needs
Electrolyte guidance for longer fasts
Activity & climate adjustments
Open calculator
Breaking your fast
Refeeding Calculator

After an extended fast, what you eat first matters as much as the fast itself. Get a personalised refeeding plan — calories, macros, timing, and what to avoid.

Post-fast calorie & macro targets
Refeeding timeline by fast length
Foods to eat and foods to avoid
Warning signs of refeeding syndrome
Open calculator
These tools are for informational purposes only. They are not a substitute for medical advice. If you have a health condition, take medication, or are unsure whether fasting is appropriate for you, speak to your healthcare provider before making changes to your routine.