THC is stored in fat
Unlike many drugs that are water-soluble and flushed relatively quickly, THC is lipophilic — it dissolves in fat. After use, THC and its metabolites are absorbed into fatty tissue throughout the body and then released back into the bloodstream slowly, over days or weeks, to be broken down and excreted. This storage-and-release cycle is the whole reason detection windows are so long and so variable.
How accumulation works
For an occasional user, a single exposure deposits a small amount that the body steadily clears. For a daily user, new THC arrives faster than the old supply is released — so fat stores fill up and stay topped off. When a frequent user finally stops, they're not starting from zero; they're starting from a deep reservoir that has to drain. That's why heavy users can test positive for 30 days or more after their last use while a first-timer is clear in a few days.
The calculator weighs your frequency and body composition to estimate how long your reservoir takes to drain below the cutoff.
Run my estimate →The body-fat factor
Because the reservoir is fat, more body fat generally means more storage capacity and a slower release — extending the window. This isn't a moral judgment about fitness; it's just where the chemistry lives. It also interacts with frequency: a lean occasional user and a higher-body-fat daily user are at opposite ends of the spectrum, and a generic "X days" estimate will be wrong for both.
Why exercise can backfire right before a test
Here's the counterintuitive part. Because metabolites are stored in fat, burning fat can release them back into circulation. Intense exercise in the days leading up to a test can temporarily raise the concentration of THC-COOH showing up in your urine. Staying active during the broader clearance period is fine — even helpful over weeks — but hard workouts in the final 24 hours before a test are a known way to nudge a borderline result in the wrong direction.
Planning around it
- ›Give yourself more runway if you're a frequent user. The reservoir is real; respect it.
- ›Taper intense exercise in the last day before a test, even if you train regularly.
- ›Test at home to watch your trend instead of guessing.
- ›Don't expect shortcuts to drain the reservoir. Only time does that.
An independent desk reviewing pharmacokinetic research and regulatory guidance from SAMHSA and DOT. Content reviewed quarterly for accuracy.