Sleep Calculator — Bedtime & Wake Time

Find the best bedtime or wake-up time based on 90-minute sleep cycles. Wake feeling refreshed.

Last updated: April 2026 · Source: NHS — How to get to sleep

Go to bed at:

21:45

9h · 6 cycles

Ideal

23:15

7.5h · 5 cycles

Ideal

00:45

6h · 4 cycles

Good

02:15

4.5h · 3 cycles

Minimum

Based on 90-minute sleep cycles. Includes 15 minutes to fall asleep.

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

Sleep occurs in cycles of approximately 90 minutes, moving through light sleep, deep sleep and REM sleep. Waking at the end of a complete cycle (rather than mid-cycle) tends to leave you feeling more rested. Most adults need 4–6 full cycles per night, corresponding to 6–9 hours of sleep.

This calculator works in two modes: enter your desired wake time to calculate optimal bedtimes, or enter your bedtime to calculate the best wake times. It factors in an average sleep-onset latency of 15 minutes (the time it takes to fall asleep) and counts back or forward in 90-minute intervals.

The NHS recommends that adults aged 18–64 aim for 7–9 hours of sleep per night. Consistently sleeping fewer than 6 hours is linked to increased risk of obesity, cardiovascular disease and impaired cognitive function. Maintaining a consistent sleep schedule is more important than the exact number of hours.

Example: Need to wake at 7:00 AM

  1. Allow 15 minutes to fall asleep
  2. 6 cycles (9 hours): bedtime 9:45 PM
  3. 5 cycles (7.5 hours): bedtime 11:15 PM
  4. 4 cycles (6 hours): bedtime 12:45 AM
  5. Recommended: 9:45 PM or 11:15 PM for optimal rest

Source: NHS — How to get to sleep

Frequently Asked Questions

What does the Sleep Calculator — Bedtime & Wake Time do?
Find the best bedtime or wake-up time based on 90-minute sleep cycles. Wake feeling refreshed. All calculations are performed in your browser using official UK rates and thresholds.
Is this medical advice?
No. This calculator is for informational purposes only and does not constitute medical advice. Always consult your GP or an appropriate healthcare professional for medical guidance.
Are the reference values from the NHS?
Where applicable, this calculator uses reference values and guidelines from the NHS and other UK health authorities. Individual needs may vary based on personal health circumstances.