Calculators
Tools that do the maths
All ten calculators are client-side, free, and show the formula behind every result. Each one is also embedded inside the relevant article — so you can read the science and run the numbers without switching pages.
Timing
Stimulants
Caffeine Half-Life Calculator
How much caffeine is in your system at bedtime, given drink type, dose, and sensitivity.
Melatonin Timing Calculator
When to take melatonin for a phase-shifting effect — which is mostly not at bedtime.
Caffeine Cut-Off Calculator
Last safe caffeine time for your target bedtime and sensitivity.
Personal
Chronotype Quiz
Validated MEQ-style assessment. Outputs your morning/evening preference and what it means.
Sleep Debt Calculator
Estimated debt over the past week, plus a recovery plan that doesn't promise you can binge-sleep it away.
Sleep Need Estimator
Quiz-style: estimates your individual sleep need based on how you function on different amounts.
Sleep Efficiency Calculator
Time-in-bed vs time-asleep ratio, with a CBT-I-aware interpretation.