The short answer
THC and its metabolites can stay detectable anywhere from a few hours to 90 days after last use — but that enormous range collapses fast once you know two things: which test you're facing, and how often you use. The test type sets the ceiling; your habits and body set where you land inside it.
Notice how different these are. A saliva swab and a hair test can be looking at the same person and reach opposite conclusions, because they measure completely different things over completely different time spans. The first question to answer is never "how long does THC last" — it's "which test am I taking?"
What actually sets your timeline
Within a given test type, four variables do most of the work:
- ›Frequency of use. The single biggest factor. Daily use builds up stored metabolites; a one-time use barely registers by comparison.
- ›Body fat. THC's main metabolite is fat-soluble. More adipose tissue means more storage and a slower release.
- ›Metabolism & activity. How quickly your body processes and excretes the compound.
- ›Potency and dose. Higher-THC products leave more behind to clear.
This is why generic timelines fail people. "Two weeks" is meaningless without knowing whether you're a first-timer with low body fat or a daily user — those two people can be weeks apart.
By test type
Saliva catches recent use — generally the last day or two, sometimes up to 72 hours for heavy users. It's increasingly common for roadside and some pre-employment screens because it's quick and hard to tamper with.
Blood is the most direct measure of active THC and clears quickly, which is why it's used mostly in DUI and accident investigations rather than employment.
Urine is the workplace standard. It detects the inactive metabolite THC-COOH, not THC itself, at a 50 ng/mL cutoff — and because that metabolite is stored in fat, the window stretches from a few days to a month or more.
Hair has the longest reach: a standard 1.5-inch sample reflects roughly 90 days of history. It's less sensitive to a single recent use but very hard to beat for chronic users.
Our calculator factors your weight, body fat, frequency, and test type into an estimated clearance date — free, no signup to see it.
Run my estimate →Single use vs. chronic use
For a urine test at the 50 ng/mL cutoff, the spread looks roughly like this: a true first-time, single use often clears in 1–3 days; occasional use (a couple times a week) in 3–7 days; regular use (most days) in 1–3 weeks; and daily or heavy use can take 30 days or more. The reason is accumulation — chronic use saturates fat stores faster than the body releases them, so the "clock" only really starts once intake stops.
How to find your number
Averages are a starting point, not a plan. The practical move is to estimate your window from your inputs, then confirm with an inexpensive at-home test a few days before the real one. If the at-home strip reads negative at the same cutoff the lab uses, you have real evidence — not a guess from a forum.
Quick answers
Does THC leave faster if you exercise? Not reliably, and intense exercise right before a test can briefly raise urine levels by mobilizing fat stores. Do detox drinks work? At best they dilute temporarily; labs flag dilute samples. Can secondhand smoke make you fail? Extremely unlikely under realistic conditions at standard cutoffs.
An independent desk reviewing pharmacokinetic research and regulatory guidance from SAMHSA and DOT. Content reviewed quarterly for accuracy.