How Long Does Weed Stay in Your System?

Weed can be detectable for about 1–90 days or longer after last use, depending on the test, frequency and amount of use, and individual metabolism. Use the thc detox calculator for a rough estimate, not a guaranteed test result. For more on what does and does not affect elimination, see how to detox from weed.

How long is weed detectable on different tests?

The ranges below are approximate, not deadlines for passing a test. Labs may look for THC, the main intoxicating compound in weed, or for its metabolites, which are substances produced as the body processes it.

Urine tests commonly look for a THC metabolite rather than active THC. A positive urine result can therefore persist after the intoxicating effects have ended; it cannot establish current impairment by itself.

Hair testing reflects a longer period and depends partly on the length of hair collected. It may miss a single use or very recent use, so a negative hair result does not prove that someone never used weed during the period covered.

These ranges can overlap, and an individual result may fall outside them. A laboratory’s cutoff—the minimum concentration reported as positive—and whether it performs a confirmation test also affect the result.

What changes how long weed stays detectable?

Frequency and amount matter. Repeated use can lead to longer detection than a single use because THC and its metabolites can accumulate with ongoing exposure. Product strength and the amount used also influence exposure, although they cannot predict an exact result.

The test and what it measures matter. Blood and saliva tests may measure active THC, while urine tests usually target a metabolite. Different laboratories and testing programs may use different cutoffs, so the same sample could be interpreted differently under different rules.

Individual processing varies. THC is fat-soluble, and the body can release stored THC gradually. Metabolism, body composition and health can affect the process, but none lets you calculate a reliable clearance date on its own.

The way weed is used matters too. An edible may take longer to produce effects and those effects may last longer than with smoked weed. That does not translate into a dependable rule for when a particular test will be negative.

What is the half-life of weed?

A half-life describes the time it takes for the amount or concentration of a substance to fall by half under specified conditions. There is no single half-life that tells everyone when weed will no longer be detectable: THC and its metabolites behave differently, and the measured rate changes with the sample, timing and pattern of use.

Even when a concentration falls, a test can remain positive until it drops below that test’s cutoff. A half-life is therefore not the same as a detection window, and multiplying it by a fixed number does not guarantee a negative result.

Can a calculator tell you when weed will be undetectable?

A calculator can offer a broad estimate based on inputs such as the last use and how often weed was used. It cannot measure your current THC or metabolite concentration, account for every laboratory cutoff or promise that you will pass a test.

For a test with employment, legal or medical consequences, check which sample and cutoff the testing program uses. If you need to understand a result, ask the testing provider or a clinician rather than relying on an estimated date.

Who should be careful, and when should you seek help?

If you are pregnant or breastfeeding, have a heart condition, or take sedating medication, discuss weed use with a clinician. Do not stop prescribed medication on your own. A clinician can also help if weed use is causing anxiety or interfering with daily life.

Contact Poison Control promptly if a child may have consumed weed. Seek emergency help for trouble breathing, a seizure, severe confusion, chest pain, or if someone cannot be awakened. Do not drive while impaired.