What these calculators work out
Put your weight and activity level into the Water Intake Calculator, work a bedtime backwards from your alarm with the Sleep Cycle Calculator, or check what an hour of cycling actually costs you in the Calorie Burn Calculator. Runners get a Running Pace Calculator and a Race Time Predictor that turns a recent 5K into a realistic marathon target, plus a Target Heart Rate Calculator for zone training and a Bike Gear Ratio Calculator when you are rethinking your gearing.
Cycles, dates and outdoor plans
If you are tracking a cycle or a pregnancy, the Ovulation Calculator and Due Date Calculator do the counting for you from your last period date. For time spent outside, the Wind Chill and Heat Index Calculator tells you how the air will really feel, while the Sunrise and Sunset Calculator and the Moon Phase Viewer help you plan around the light. There is also a Plant Watering Schedule and a Printable Habit Tracker for the routines around all of it.
Your numbers stay with you
Nothing you type leaves your device. Every number is worked out on your own phone or computer, so your weight, your last period date and your training paces are never sent to us, saved to an account or remembered once you close the tab. These are health and fitness calculators with no signup, and no email address is needed to see your result.
Frequently asked questions
How much water should I drink a day?
Most adults need roughly 2.7 to 3.7 litres of total fluid a day, and a common personalised starting point is about 35 ml per kilogram of body weight. Roughly a fifth of that comes from food, so drinking targets are usually lower than total intake figures. Add fluid for exercise, heat, altitude and illness. The Water Intake Calculator applies these adjustments to your own weight and activity level.
How does a sleep cycle calculator decide when I should go to bed?
It counts backwards from your wake time in roughly 90 minute blocks, because a full sleep cycle averages about 90 minutes and waking at the end of one leaves you less groggy than waking mid cycle. Most adults do best on four to six complete cycles, or six to nine hours. The Sleep Cycle Calculator also adds about 15 minutes for the time it usually takes you to actually drop off.
Is my health data private when I use these calculators?
Yes. Every tool here does its work on your own phone or computer, so the values you enter, including your weight, cycle dates, due dates and training paces, are never sent to us. There is no account and no login, nothing you type is stored, and closing the tab throws it all away. That matters most for the Ovulation Calculator and Due Date Calculator, where the inputs are genuinely sensitive.