THC Detection Calculator
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Every estimate is based on peer-reviewed toxicology research, not guesswork.
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About this calculator
What it estimates: a personalized urine THC detection window at two thresholds — Standard (50 ng/mL, the common workplace cutoff) and Confirmatory (15 ng/mL, a more sensitive lab-grade cutoff).
What it's based on: peer-reviewed toxicology research, reviewed by Dr. Matthew Nuesse, DOT Certified Medical Examiner.
What it doesn't do: it doesn't estimate blood, saliva, or hair detection windows, and it isn't a substitute for an actual test — individual results vary based on physiology, hydration, and metabolism.
Why we ask what we ask: each question — age, body type, usage frequency, duration of use, and lifestyle factors — directly affects how quickly THC clears your system. More accurate answers give a more personalized estimate.
Read the full methodology →*Your answers are stored securely, never shared with third parties, and used only for research purposes.
Prolonged retention beyond this estimate has been documented in extreme chronic-use cases. Consider an at-home confirmatory test before relying on this range alone.
| Urine Test Cutoff | Estimated Window | Notes |
|---|
Estimates are based on peer-reviewed toxicology research and population averages (Huestis 2007; Goodwin et al. 2008; SAMHSA cutoff guidelines). Individual results vary by physiology, hydration, and metabolism. This tool is informational only and is not medical or legal advice.
50 ng/mL and 15 ng/mL are standard federal screening and confirmation cutoffs (49 CFR Section 40.85).
How long does THC stay in your system?
The answer depends on three things: how often you use, which test is used, and the cutoff that test is set to. For a standard 50 ng/mL urine test, a one-time user is usually clear within about 1 to 3 days. Occasional users tend to test positive for 3 to 7 days, regular users for 1 to 2 weeks, and daily users for around 10 to 21 days.
Long-term heavy users are the exception and can stay positive for a month or more, because THC builds up in body fat and leaves slowly [1][4]. These are research-based estimates, and your own timeline may be shorter or longer depending on your body and your habits.
Detection window by cutoff level
| Usage pattern | 20 ng/mL (strict) | 50 ng/mL (standard workplace) | 100 ng/mL (lenient) |
|---|---|---|---|
| One-time use | 2 to 5 days | 1 to 3 days | 1 to 2 days |
| Occasional, up to once a week | 4 to 8 days | 3 to 7 days | 2 to 5 days |
| Regular, a few times a week | 10 to 18 days | 7 to 14 days | 5 to 10 days |
| Daily | 18 to 30 days | 10 to 21 days | 7 to 14 days |
| Heavy, several times a day | 46 to 77 days | 30 to 45 days | 21 to 30 days |
The cutoff is the concentration at which a test reports positive. A lower number means the test reacts to smaller traces, so a 20 ng/mL test stays positive longer than a 50 or 100 ng/mL test for the same person [1]. The 50 ng/mL level is the standard set by SAMHSA for federal workplace screening, with lab confirmation done at 15 ng/mL [2][3]. The longest windows apply to heavy daily users under monitored abstinence; one group of chronic users still tested positive at low cutoffs for up to 77 days after their last use [4]. Most people fall well short of that.
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Test-type explanations (urine vs. oral fluid vs. hair vs. blood)
Urine THC tests (most frequent)
Urine testing is the most common method, and it is what our strips are built for. It does not measure the THC that gets you high. It looks for THC-COOH, an inactive metabolite your body makes as it breaks THC down, which is why a positive result shows past use rather than current impairment [1].
Standard workplace screening uses a 50 ng/mL cutoff, and if a sample screens positive, it goes to a lab for confirmation at 15 ng/mL [2][3]. Detection windows go from a day or two for a one-time user to several weeks for a daily user, with the table above showing the ranges by cutoff. Because THC is stored in fat and released gradually, frequent users clear it far more slowly than occasional users [1][4].
Saliva (oral fluid) THC tests
A saliva test, also called an oral fluid test, catches recent use. It is often chosen for roadside checks and some workplace programs because it points to use within roughly the last day rather than the last month.
For occasional users, the window is short, often under 24 hours. For frequent users, THC has been detected in oral fluid for around 72 hours after last use [1]. Federal oral fluid guidelines confirm a positive at 2 ng/mL for THC [5]. This test says more about when you last used than how much is in your system.
Blood THC tests
Blood testing has the shortest window of the common methods and is mostly used in research or impaired-driving cases. Active THC in blood drops quickly after use, detectable for a matter of hours in occasional users. In heavy chronic users, it can linger longer, and one study still found THC in the blood of frequent users well into a monitored abstinence period [6]. Because it measures active THC, blood is the method most tied to recent use rather than past use.
Hair THC tests
Hair testing has the longest lookback, commonly cited as about 90 days, because THC traces are laid down in the hair shaft as it grows [1]. It is rarely used for routine employment screening. It can miss lighter or infrequent users, and questions about external contamination and fairness across hair types mean it is treated with more caution than urine testing. For most people preparing for a standard test, hair testing is not the concern.
What changes your THC detection time
How often you use
Frequency is the biggest factor by far. A one-time user and a daily user are not in the same range. One clears in days, the other in weeks. THC is fat-soluble, so repeated use builds up in body fat faster than the body clears it, then releases slowly once you stop [1]. When you use the calculator, enter your real pattern over the past month, not just your last session.
The cutoff the test uses
The same person on the same date can pass or fail depending on the test's cutoff. A lower cutoff detects smaller traces, so it stays positive longer [1]. A 20 ng/mL test detects longer than a 100 ng/mL one. Workplace screens are usually 50 ng/mL, with lab confirmation at 15 ng/mL [2][3]. Knowing your test's cutoff matters as much as knowing your own habits.
Your body composition
Body composition and metabolism play a smaller role than frequency or cutoff. Because THC is stored in fat, body-fat percentage affects how much builds up and how slowly it clears [1], and metabolic rate and liver function influence the pace too. This is why two people with identical habits can clear on different timelines, and why the calculator gives a range.
What you used and how much
Dose and strength matter as well. A strong concentrate or edible loads far more THC than a low-potency product, so there is more to clear. Edibles can also stretch the urine window slightly compared with smoking the same amount, since oral dosing shifts how the metabolite appears [1]. There is no reliable shortcut. Drinking large amounts of water only dilutes a sample briefly and can get it rejected as too dilute.
Which cutoff should I test at?
The right cutoff is the one that matches the test you are preparing for. Most workplace urine screens are set at 50 ng/mL, so a home strip at that same level gives you the closest read on whether you would pass [2][3].
If you want more than a yes-or-no answer, a multi-level test checks 20, 50, and 100 ng/mL at once, so you can see not just whether you are positive but how close you are to each line. That is useful when you are counting down to a test date and want to watch the trend as you get clearer, rather than testing blind.
Can I test myself at home before a real test?
Yes, and it is the most direct way to take the guesswork out of it. An at-home urine strip uses the same method and cutoff as a standard lab screen, so testing yourself the morning of, or in the days leading up to, a real test gives you a realistic preview.
If you see a faint line, that still counts as negative for that cutoff, since any line in the result window means THC is below the threshold. Testing over several days also shows which direction you are heading, which matters more than any single result.
Frequently Asked Questions
How long does weed stay in your urine?
For a 50 ng/mL urine test, most one-time users are clear within 1 to 3 days, occasional users within a week, and regular users within about two weeks. Daily users usually need 10 to 21 days, and long-term heavy users can stay positive for a month or more because THC accumulates in fat and clears slowly [1][4]. Your habits over the past month matter more than any single session.
How long does one hit stay in your system?
For someone who genuinely used only once, a single hit usually clears a 50 ng/mL urine test in about 1 to 3 days. The catch is that "one hit" only behaves that way if you had not used in the weeks before. If you had, your body is clearing the earlier buildup too, and your window looks like an occasional or regular user's rather than a first-timer's [1].
How long do edibles stay in your system?
Edibles are broken down into the same THC-COOH that urine tests look for, so the detection windows are broadly similar to smoking. Taking THC by mouth can stretch the urine window a little compared with inhaling the same dose, because of how the metabolite is produced and cleared after oral intake [1]. As with anything else, the dose you took matters more than the format.
Does the cutoff (20, 50, or 100 ng/mL) change how long THC shows up?
Yes, and the effect is significant. A lower cutoff reacts to smaller traces, so it keeps testing positive after a higher cutoff has gone clear [1]. For the same person and the same last-use date, a 20 ng/mL test can stay positive noticeably longer than a 100 ng/mL one. This is why knowing your test's cutoff is as useful as knowing your own pattern.
Do Delta-8 or HHC show up on a drug test?
Usually, yes. They break down into metabolites close enough to regular THC that standard urine immunoassays flag them the same way, and most screens cannot tell Delta-8 apart from Delta-9 [1]. Labels like "hemp-derived" or "legal in my state" describe the law, not the chemistry, and they do not change what the test detects.
Will CBD make me fail a drug test?
Pure CBD isolate should not, because tests target THC and its metabolite rather than CBD. The risk comes from the product. Full-spectrum and broad-spectrum CBD can contain trace THC, legally up to 0.3%, and steady use of those products has caused positive results. If you are being tested, a verified isolate is the safer choice.
Can you flush THC out faster?
No method reliably flushes THC quickly. Drinking a lot of water before a test only dilutes your urine for a short time, and labs check for that; a sample that looks too dilute can be rejected and treated as a failed or invalid test. Time and not using are the only dependable ways to clear, which is why testing yourself in advance is more useful than any detox product.
Can I test myself at home before a real test?
Yes. A home urine strip at the same cutoff as your upcoming test gives you a realistic preview of the result. Testing across several days shows the trend as you clear, and a multi-level strip shows how close you are to each threshold rather than a single pass-or-fail answer.
Sources
- Huestis MA. Human Cannabinoid Pharmacokinetics. Chemistry & Biodiversity. 2007;4(8):1770–1804. Covers metabolism, fat storage, the THC-COOH metabolite, dosing route effects, and detection-window behavior. Check this source.
- SAMHSA / HHS. Mandatory Guidelines for Federal Workplace Drug Testing Programs. Federal Register, 82 FR 7920 (Jan 23, 2017). Establishes the 50 ng/mL urine screening cutoff and 15 ng/mL confirmatory cutoff for marijuana. Check this source.
- SAMHSA / HHS. Mandatory Guidelines for Federal Workplace Drug Testing Programs, Authorized Testing Panels. Federal Register, 91 FR 12308 (Mar 13, 2026). Reaffirms the current federal urine panel, including the 50 ng/mL marijuana screening cutoff, with no changes to analytes or cutoffs. Check this source.
- Ellis GM Jr, Mann MA, Judson BA, Schramm NT, Tashchian A. Excretion patterns of cannabinoid metabolites after last use in a group of chronic users. Clinical Pharmacology & Therapeutics. 1985;38(5):572–578. Basis for the up-to-77-day figure in chronic users under supervised abstinence. Check this source.
- SAMHSA / HHS. Mandatory Guidelines for Federal Workplace Drug Testing Programs, Oral/Fluid. Federal Register, 84 FR 57554 (Oct 25, 2019). Oral fluid confirmatory cutoff of 2 ng/mL for THC and detection findings in occasional vs frequent users. Check this source.
- Bergamaschi MM, et al. Plasma cannabinoid detection windows in frequent cannabis smokers during sustained abstinence, with 11-OH-THC detected up to 15 days after admission. PMC. Documents THC persistence in the blood of frequent users during monitored abstinence. Check this source.
