How to Use the Caffeine Bedtime Calculator
Almost everyone has lain awake at night wondering why that afternoon coffee is still keeping them up. Caffeine doesn't leave your system instantly — it breaks down gradually over its half-life, roughly 5-6 hours. This calculator uses your intake time to estimate how much caffeine remains in your body over time, and tells you a safe bedtime that won't fight against your sleep.
For example, if you had coffee at 3:00 PM and your half-life is 5.5 hours, about half the caffeine is still in your system around 8:30 PM, and it doesn't drop to roughly 25% until around 2:00 AM. If you're caffeine-sensitive, your half-life can run even longer, meaning a single late cup can leave you more alert than you'd expect well into the night.
A common guideline for good sleep is to stop caffeine at least 8-10 hours before bed. Use this calculator to see when today's coffee stops meaningfully affecting your sleep, and if you're sensitive to caffeine, consider switching to decaf or herbal tea after early afternoon.
Frequently Asked Questions
For most adults it's roughly 5-6 hours, though it varies a lot based on smoking, pregnancy, or certain medications. If you're sensitive to caffeine, your half-life can run longer, sometimes 7 hours or more.
After one half-life, half the caffeine remains. After two, only about 25% is left. That level is generally considered low enough to avoid meaningfully disrupting sleep for most people, which is why it's used as the safe threshold.