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Sleep & Recovery Calculators

Plan your sleep, caffeine timing, and recovery with evidence-informed tools for bedtimes, HRV readiness, and related metrics.

Sleep, Caffeine, and Recovery as a System

Sleep is a system, not a single variable. The body repeats roughly 90-minute cycles through light sleep, slow-wave (deep) sleep, and REM, with deep sleep concentrated in the first half of the night and REM lengthening toward morning. Waking in the middle of a deep-sleep segment tends to feel groggier than waking at the end of a cycle, which is why bedtime and wake-time planning based on cycles can feel meaningfully different from just counting hours. The 2021 American Academy of Sleep Medicine consensus recommends at least 7 hours per night for most adults, but how those hours are distributed — how consistent your schedule is, when you consume caffeine, how much light and temperature support the wind-down — often matters as much as the number itself.

Caffeine is the lever most people can actually pull. Pharmacokinetic studies place caffeine’s average half-life in healthy adults at about five hours, with a range of roughly three to nine hours depending on liver enzyme genetics (CYP1A2), hormonal status, pregnancy, oral contraceptive use, and smoking. A late-afternoon coffee can therefore leave 50–75 mg of caffeine in your system at bedtime — enough to reduce slow-wave sleep and total sleep time on polysomnography, even when people report they “feel fine.” Recovery signals like heart rate variability (HRV) track how your autonomic nervous system is balancing stress and rest. Research on athletes suggests that HRV responds predictably to alcohol, training load, and poor sleep, and most evidence-informed readiness systems compare your current HRV against a rolling personal baseline rather than a population norm.

Sleep and recovery numbers work best as trend indicators, not diagnoses. Chronic insomnia, persistent daytime sleepiness, loud snoring with pauses, or a sudden drop in recovery metrics despite stable training and lifestyle all deserve a conversation with a clinician — possibly a sleep study to rule out apnea or another disorder. These tools are for informational purposes only and are not a substitute for professional medical advice.

How These Calculators Relate

Start the day-of-planning with the Sleep Calculator to pick a bedtime or wake time that ends on a full cycle. Back that up with the Caffeine Sleep Optimizer to estimate how much caffeine will still be circulating at your target bedtime and to choose a realistic cutoff. Over the week, use the Sleep Debt Calculator to make accumulated shortfalls visible, and the Recovery Score Calculator to roll HRV, resting heart rate, sleep, and subjective readiness into a single trend you can train against.

Caffeine Sleep Optimizer

Estimate residual caffeine at bedtime and a safe cutoff time using a 5-hour half-life decay model.

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Frequently Asked Questions

How long is one sleep cycle?
A typical sleep cycle is about 90 minutes and moves through light sleep, deep sleep, and REM. Real cycles vary from roughly 70 to 120 minutes, and they get longer and more REM-heavy as the night goes on, which is why the second half of a full night of sleep is often the most restorative.
When should I cut off caffeine before bed?
Caffeine has an average half-life of about five hours in healthy adults, though it can range from three to nine hours depending on genetics, hormonal status, smoking, and medications. A common rule of thumb is to stop caffeine at least 8 to 10 hours before your target bedtime, which is what the Caffeine Sleep Optimizer estimates.
What does HRV tell me about recovery?
Heart rate variability (HRV) reflects autonomic nervous system balance and often drops after hard training, alcohol, poor sleep, or illness. Tracking your HRV trend against your own baseline — rather than comparing to other people — is the common evidence-informed approach for gauging recovery readiness.
Is 6 hours of sleep enough?
The 2021 American Academy of Sleep Medicine consensus recommends at least 7 hours of sleep per night for adults. Chronic sleep below that is associated in observational research with higher rates of cardiometabolic disease and poorer cognitive performance. Individual needs vary, but most people who think they thrive on 6 hours show measurable deficits on objective testing.
What is sleep debt?
Sleep debt is the running total of sleep you have missed against your own target over several nights. A single short night can usually be recovered from with a longer following night, but chronic debt accumulates and is harder to fully repay — the Sleep Debt Calculator gives a 7-day view to make the pattern visible.