When Should You Stop Drinking Coffee Before Bed?

There’s no single number — it depends on your personal half-life. As a rule of thumb, stop when a cup would still leave more than ~50 mg in your system at bedtime. For most people that’s 6–10 hours before bed; the calculator gives you the exact time.

Decaf still contains a small amount of caffeine — typically 2–5 mg per cup versus ~95 mg for regular. For most people that’s negligible at night, but very sensitive or slow metabolizers may still notice it.

Caffeine follows first-order decay with a half-life of roughly 3–9 hours. After one half-life, half remains; after two, a quarter. It can take 10+ hours to clear most of a single coffee — longer if you’re a slow metabolizer, pregnant, or on oral contraceptives.

Sometimes — it depends on the dose, the timing, and your sensitivity. The calculator shows how many mg would still be on board at bedtime so you can decide whether that last cup is worth it.