Blue Light Bedtime Calculator
When to stop screens before bed for better sleep.
Enter your values
Enter the bedtime hour (24h) you are working with.
Enter the bedtime minute you are working with.
Enter the screen cut-off lead in min.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Stop screens at
- 21:30
- Last caffeine
- 15:00
- Last large meal
- 20:00
- Dim lights from
- 21:00
Quick answer
Melatonin release is suppressed by evening light, so a screen cut-off 60-120 minutes before bed helps sleep onset.
cut-off = bedtime - recommended lead time
At a glance
| What it does | When to stop screens before bed for better sleep. |
|---|---|
| Category | Health |
| Inputs needed | Bedtime hour (24h), Bedtime minute, Screen cut-off lead |
| Main output | Stop screens at |
| Formula | cut-off = bedtime - recommended lead time |
| Cost | Free — no sign-up, no download |
How to use the Blue Light Bedtime Calculator
- 1Enter the bedtime you are aiming for.
- 2Choose a screen cut-off lead of 60-120 minutes.
- 3Dim household lighting at the same time for a stronger effect.
Inputs explained
- Bedtime hour (24h)
- Enter the bedtime hour (24h) you are working with.
- Bedtime minute
- Enter the bedtime minute you are working with.
- Screen cut-off lead(min)
- Enter the screen cut-off lead in min.
Worked example
Using the values the calculator loads with:
Inputs
- Bedtime hour (24h)23
- Bedtime minute0
- Screen cut-off lead90 min
Results
- Stop screens at21:30
- Last caffeine15:00
- Last large meal20:00
- Dim lights from21:00
Frequently asked questions
Do night-shift filters help?
They reduce blue light but not brightness or mental stimulation — dimming and stopping matter more.
Is 8 hours the right caffeine cut-off?
Caffeine's half-life is about five hours, so eight hours leaves roughly a third in your system.
What do I need to enter into the Blue Light Bedtime Calculator?
Just 3 values: bedtime hour (24h), bedtime minute, screen cut-off lead. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Blue Light Bedtime Calculator work out the answer?
Melatonin release is suppressed by evening light, so a screen cut-off 60-120 minutes before bed helps sleep onset. It applies the formula cut-off = bedtime - recommended lead time and shows the working so you can check each step by hand.
Is the Blue Light Bedtime Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.