How the math works
Caffeine leaves your body on a curve, not a schedule. Every half-life, the amount in your blood drops by half.
For the average adult that half-life is about 5 hours. The FDA cites a typical range of 4 to 6, and the true spread runs from under 2 hours to over 9 depending on your genes, medications, and whether you smoke.
So a 95mg cup at 2pm doesn't "wear off" by dinner. At a 5-hour half-life you're at about 48mg at 7pm, 24mg at midnight, and 12mg at 5am.
The calculator above just runs that arithmetic for every dose you log and adds the curves together. No account, no tracking, nothing stored.
What to do with the bedtime number
There's no single "safe" threshold, but the useful frame is simple: the more caffeine on board at lights-out, the harder your brain has to fight for deep sleep.
Common sleep guidance puts the last full-strength coffee 8 to 10 hours before bed. If your bedtime number keeps landing high, you have two levers.
Move the cutoff earlier, or make the afternoon dose smaller. The second lever is why half-caffeine swaps took off: our best mushroom coffee comparison covers the category, including blends that run about 80% less caffeine than a large cup.
And if caffeine isn't the only thing between you and sleep, the sleep and stress hub has everything we've researched, from breathing pacers to the Dodow sleep light.
Frequently asked questions
What is the half-life of caffeine?
About 5 hours for the average healthy adult, meaning half of what you drank is still circulating 5 hours later. The FDA cites a typical range of 4 to 6 hours, and individual clearance runs from roughly 1.5 to over 9 hours depending on genetics, medications, pregnancy, and smoking.
How long does caffeine stay in your system?
Working from a 5-hour half-life, a 95mg cup of coffee leaves about 24mg in your system after 10 hours and about 12mg after 15. As a rule of thumb, it takes around 10 hours for a normal dose to drop to a level most people stop noticing.
When should I stop drinking coffee before bed?
Most sleep guidance lands 8 to 10 hours before bedtime for a full cup. With a 10:30pm bedtime, that puts the last regular coffee around noon to 2:30pm. Smaller doses later can work: the math is what this calculator shows you.
Does mushroom coffee really have less caffeine?
It depends on the brand. Coffee-based blends can run close to a regular cup, while coffee alternatives like MUD\WTR sit around 35mg, roughly 80% less than a large cup of regular coffee, which is exactly why afternoon drinkers switch to them.