The short answer
For most people, THC is detectable in urine for 3 to 30 days after last use — but that range is too wide to plan around. The number that matters is your number, and it's driven mostly by how often you use, your body fat, and the lab's cutoff level.
What a urine test actually measures
A urine screen doesn't detect THC itself. It detects THC-COOH, an inactive metabolite your liver produces as it breaks the THC down. That distinction matters: the metabolite is fat-soluble, so it gets stored in body fat and released slowly over days or weeks — long after any effects are gone.
The standard immunoassay flags a sample at or above 50 ng/mL. A non-negative result is then sent for a GC-MS confirmation test at a lower threshold. This is why "I feel fine" has nothing to do with whether you'll pass.
The calculator factors your weight, body fat, and frequency to estimate your actual clearance date — free, no signup to see it.
Run my estimate →Why body fat changes everything
Because THC-COOH is stored in fat, people with higher body-fat percentages tend to retain detectable levels longer — and a sudden burst of intense exercise right before a test can briefly raise the concentration in your urine as fat cells release stored metabolites. Timing matters as much as the method.
Common mistakes that backfire
- ✕Chugging water the morning of — a diluted sample gets flagged and you get retested.
- ✕Intense exercise the day before — it can release stored metabolites and spike your levels.
- ✕Trusting a niacin or cranberry "flush" — neither survives a lab, and they cost you prep time.
An independent desk reviewing pharmacokinetic research and regulatory guidance from SAMHSA and DOT. Content reviewed quarterly for accuracy.