Coffee's caffeine typically keeps you awake and alert for about 3 to 6 hours after consumption. This duration corresponds to caffeine's half-life, which is the time it takes for your body to eliminate half of the caffeine ingested. The average half-life of caffeine ranges from 4 to 6 hours, but it can vary widely between 2 and 12 hours depending on individual factors such as metabolism, age, genetic makeup, caffeine tolerance, and other health conditions

. You usually start feeling the stimulating effects within 30 to 60 minutes after drinking coffee, with peak alertness occurring around this time. The alertness effect gradually diminishes over several hours but can still linger and affect sleep quality if consumed too late in the day

. For most people, caffeine's noticeable wakefulness effects last between 3 to 5 hours, but for those sensitive to caffeine, effects may last up to 8 hours or more. Regular coffee drinkers may experience shorter effects due to tolerance

. Because caffeine can remain in your system for up to 12 hours or longer, drinking coffee within 6 hours of bedtime can reduce total sleep time by about an hour and interfere with falling asleep

. To avoid sleep disruption, it is generally recommended to stop drinking coffee at least 6 hours before going to bed, or even earlier if you are sensitive to caffeine

. In summary:

• Caffeine effects peak within 30-60 minutes after drinking coffee.
• Effects last about 3 to 6 hours on average.
• Half-life of caffeine is typically 4 to 6 hours but can range from 2 to 12 hours.
• Caffeine can stay in your system up to 12 hours, affecting sleep.
• Avoid coffee at least 6 hours before bedtime to prevent sleep problems.

This variability means how long coffee keeps you awake depends on your personal sensitivity and habits