About this tool

Blue Light Curfew Calculator

Work back from your wake-up time to find when to switch on night mode, stop screens and turn the lights out tonight.

A blue light curfew calculator works backwards from your alarm to show the exact clock time you should stop using bright screens tonight. It chains four steps — alarm minus target sleep gives the time you need to be asleep, minus your sleep-onset latency gives lights-out, minus your chosen curfew gives screens-down, and an extra lead time marks when to switch devices to warm or night mode. Useful for anyone who keeps missing their intended bedtime because the wind-down never actually starts.

How to use Blue Light Curfew Calculator

1. 1

   Open Blue Light Curfew Calculator on AltFTool — it loads instantly in your browser.

2. 2

   Enter the values you already know.

3. 3

   Fine-tune the options to match your scenario.

4. 4

   Read the result and use it in your planning or reporting.

Why use Blue Light Curfew Calculator

• Backwards from the alarm

  The fixed point is your wake-up time, so the schedule reflects the sleep you actually need.

• Sleep-onset latency included

  The gap between getting into bed and falling asleep is counted, not ignored.

• Cycle-aligned option

  Shows the lights-out time that fits whole 90-minute cycles before your alarm.

Common use cases

• You have a 5:30 am flight alarm and want to know the last moment you can be scrolling and still get seven hours of sleep.
• You are trialling a 60-minute no-screens rule and want the specific time it starts each night rather than a vague 'an hour before bed'.
• Shift work moves your wake-up time around, so the whole wind-down chain has to be recalculated for each roster block.
• You want lights-out aligned to whole 90-minute sleep cycles so the alarm is less likely to land in deep sleep.

Frequently asked questions