Trying to figure out how long does weed stay in urine is a common question, but the answer is not the same for everyone. No simple calculator can predict the exact day a person’s urine test will turn negative.
Still, science can help us make a reasonable estimate. Research shows that the urine detection window for cannabis depends on several key factors, including how often someone uses it, how much they use, the strength of the cannabis, how long they have been using, whether they smoke, vape, or eat it, their body fat and activity level, and how sensitive the urine test is.
This article uses findings from published studies to build a simple estimation method. It is designed for general learning and rough planning only, not for legal, medical, workplace, or court-related decisions.
What urine tests usually look for
Most urine tests do not look for the feeling of being high. They usually look for THCCOOH, an inactive THC metabolite.
THC is the main chemical in cannabis that causes the high. After THC enters the body, the liver changes it into other chemicals. One important chemical is THCCOOH. This chemical can stay in urine longer than the high lasts.
THC is fat-soluble. That means it can move into body fat and slowly come back out over time. This is one reason frequent users can test positive for much longer than one-time users.
What the studies show
Here are the main scientific points used for this calculator:
| Study finding | What it means for the calculator |
|---|---|
| In a controlled smoking study, one smoked cannabis cigarette produced average last-positive urine times of about 34 hours for a lower THC dose and about 89 hours for a higher THC dose at a 15 ng/mL THCCOOH cutoff. | One-time use is often measured in days, not weeks. |
| In monitored abstinence, 60 cannabis users gave 6,158 urine samples. Mean last-positive times were 4.3, 9.7, and 15.4 days depending on starting creatinine-normalized THCCOOH level. | Heavier starting body load means longer detection. |
| In 86 chronic users, the mean excretion time was 27 days. Some stayed positive for 46 straight days, and one endpoint took up to 77 days. | Heavy chronic users can have a long tail. |
| In frequent and infrequent users, creatinine-normalized urine curves were smoother than raw urine concentration curves. Infrequent users had last positive specimens around 4 days at a 15 ng/mL cutoff; frequent users around 17 days. | Frequency matters a lot. |
| In heavy users, urinary metabolite half-life ranged from 0.8 to 9.8 days, with a mean of 3.0 days. | Heavy users vary a lot. |
| THC is highly fat-soluble. Inhaled THC bioavailability is about 10%-35%; oral THC bioavailability is lower, about 4%-12%. | Route and body storage matter. |
| Exercise caused a small rise in blood THC in regular users, and the rise was linked with BMI. | Activity/body fat may matter, but this is a weak urine predictor. |
Because of these findings, the calculator uses a score instead of pretending to know the exact urine THCCOOH level.
The basic idea
The calculator estimates a “Cannabis Load Score.”
The score is not a real lab value. It is a rough way to turn user information into a detection-window group.
The formula is:
Cannabis Load Score =
Dose Score x Frequency Factor x Duration Factor x Route Factor
Then we adjust the result:
Final Estimate =
Base Range x Body Factor x Activity Factor x Test Factor
Step 1: Estimate THC per day
First, estimate how much THC is in the cannabis used each day.
Use this formula:
THC mg per day = grams per day x 1000 x THC strength
Use THC strength as a decimal:
| Strength | Use this number |
|---|---|
| Low strength flower | 0.08 |
| Medium strength flower | 0.12 |
| Strong flower | 0.20 |
| Very strong flower | 0.25 |
| Concentrate | 0.50-0.80 |
Example:
1.5 grams per day x 1000 x 0.12 = 180 mg THC in the flower per day
Important: this does not mean the body absorbs all 180 mg. Inhaled THC bioavailability is often about 10%-35%. The number is used only to estimate the person’s use level.
Step 2: Convert THC per day into Dose Score
Dose Score = THC mg per day / 50
Then keep it between 0.2 and 8.
Examples:
| THC in product per day | Dose Score |
|---|---|
| 10 mg | 0.2 |
| 25 mg | 0.5 |
| 50 mg | 1.0 |
| 100 mg | 2.0 |
| 150 mg | 3.0 |
| 200 mg | 4.0 |
| 300 mg | 6.0 |
| 400+ mg | 8.0 |
Step 3: Add Frequency Factor
| Use frequency | Frequency Factor |
|---|---|
| Once | 0.25 |
| 1-2 days per week | 0.40 |
| 3-4 days per week | 0.65 |
| 5-6 days per week | 0.85 |
| Every day | 1.00 |
| Many times every day | 1.15 |
Step 4: Add Duration Factor
How long the person has used at this pattern matters. Longer use gives the body more time to build a stored THC/metabolite pool.
| Time using this pattern | Duration Factor |
|---|---|
| One time only | 0.50 |
| Less than 1 month | 0.70 |
| 1-3 months | 0.90 |
| 3-12 months | 1.00 |
| 1-3 years | 1.15 |
| More than 3 years | 1.30 |
Step 5: Add Route Factor
| Main route | Route Factor |
|---|---|
| Smoked flower | 1.00 |
| Vaped flower | 1.15 |
| Edibles | 1.20 |
| Concentrates / dabs / carts | 1.50 |
| Mixed methods | 1.20-1.50 |
Why? Controlled studies show route matters. Vaporized cannabis can produce higher urine THCCOOH than the same THC dose smoked. Oral cannabis can also have a different and longer pattern.
Step 6: Find the base detection range
Now calculate:
Cannabis Load Score =
Dose Score x Frequency Factor x Duration Factor x Route Factor
Then use this table:
| Cannabis Load Score | User type | Base urine estimate |
|---|---|---|
| Less than 0.3 | Very light / one small use | 1-3 days |
| 0.3-0.8 | Light occasional use | 2-5 days |
| 0.8-1.5 | Moderate occasional use | 4-10 days |
| 1.5-3.5 | Regular use | 7-18 days |
| 3.5-6.0 | Daily or near-daily use | 14-35 days |
| 6.0-9.0 | Heavy daily use | 25-50 days |
| More than 9.0 | Very heavy chronic use | 35-77+ days |
This table is the heart of the method. It is calibrated to the published urine studies, especially the controlled single-use studies, the monitored abstinence studies, and the chronic-user studies.
Step 7: Adjust for body type
This part is weaker than the use-pattern part. We know THC is fat-soluble, but studies do not give a perfect urine formula for body fat.
Use a small adjustment only:
| Body type | Body Factor |
|---|---|
| Lean / low body fat | 0.90 |
| Average | 1.00 |
| Higher body fat | 1.15 |
| Obese or very high body fat | 1.25 |
Step 8: Adjust for lifestyle activity
Activity is not magic. There is no strong proof that exercise quickly clears urine faster. One study found exercise can raise blood THC a little in regular users, likely because THC can come out of fat stores.
So use only a small activity factor:
| Lifestyle | Activity Factor |
|---|---|
| Very active most days | 0.95 |
| Average activity | 1.00 |
| Mostly sedentary | 1.10 |
Do not overuse this factor. Frequency and amount matter much more.
Step 9: Adjust for test sensitivity
Different tests use different cutoffs.
| Test type | Test Factor |
|---|---|
| Higher cutoff screen, about 50 ng/mL | 0.80 |
| Common screen plus confirmation | 1.00 |
| Sensitive confirmation, about 15 ng/mL | 1.10 |
| Very sensitive test, below 15 ng/mL | 1.25 |
If the person does not know the test type, use 1.00.
Step 10: Calculate the final range
Multiply the base range by the body, activity, and test factors:
Final low estimate =
base low x body factor x activity factor x test factor
Final high estimate =
base high x body factor x activity factor x test factor
Round to whole days.
Example 1: daily medium flower, 1-2 grams per day
User information:
- smoked flower
- medium strength
- 1-2 grams per day, use 1.5 g as the middle
- every day
- used for 1 year
- average body type
- average activity
- unknown test, use 1.00
Step 1:
THC mg per day = 1.5 x 1000 x 0.12 = 180 mg
Step 2:
Dose Score = 180 / 50 = 3.6
Step 3-5:
Frequency Factor = 1.00
Duration Factor = 1.15
Route Factor = 1.00
Step 6:
Cannabis Load Score = 3.6 x 1.00 x 1.15 x 1.00 = 4.14
A score of 4.14 falls into:
Daily or near-daily use = 14-35 days
Step 7-10:
Body Factor = 1.00
Activity Factor = 1.00
Test Factor = 1.00
Final estimate = 14-35 days
Plain answer:
For this person, a rough urine detection estimate is about 2-5 weeks. Some people may clear faster. Heavy long-term users may take longer.
Example 2: same user, but passive lifestyle and higher body fat
Same use pattern:
- 1.5 g per day
- medium strength
- every day
- 1 year
But now:
- higher body fat: 1.15
- mostly sedentary: 1.10
- unknown test: 1.00
Base range:
14-35 days
Adjustment:
14 x 1.15 x 1.10 = 17.7
35 x 1.15 x 1.10 = 44.3
Final estimate:
18-44 days
Plain answer:
For this person, a rough estimate is about 3-6 weeks.
Example 3: active person, 0.5 g per day, 3-4 days per week
User information:
- smoked flower
- medium strength
- 0.5 g per day on use days
- 3-4 days per week
- used for 6 months
- lean body type
- very active
- unknown test
Step 1:
THC mg per use day = 0.5 x 1000 x 0.12 = 60 mg
Step 2:
Dose Score = 60 / 50 = 1.2
Step 3-5:
Frequency Factor = 0.65
Duration Factor = 1.00
Route Factor = 1.00
Cannabis Load Score = 1.2 x 0.65 x 1.00 x 1.00 = 0.78
Base range:
Light occasional use = 2-5 days
Adjust:
Body Factor = 0.90
Activity Factor = 0.95
Test Factor = 1.00
2 x 0.90 x 0.95 = 1.7
5 x 0.90 x 0.95 = 4.3
Final estimate:
2-4 days
Plain answer:
This person may be closer to a few days, not weeks. But repeated use can still make the window longer than a single use.
Example 4: very heavy concentrate use
User information:
- carts or dabs
- high THC concentrate
- equal to about 300 mg THC product per day
- many times every day
- more than 3 years
- average body
- sedentary
- sensitive test
Step 1-6:
Dose Score = 300 / 50 = 6
Frequency Factor = 1.15
Duration Factor = 1.30
Route Factor = 1.50
Cannabis Load Score = 6 x 1.15 x 1.30 x 1.50 = 13.46
Base range:
Very heavy chronic use = 35-77+ days
Adjust:
Body Factor = 1.00
Activity Factor = 1.10
Test Factor = 1.10
35 x 1.00 x 1.10 x 1.10 = 42.4
77 x 1.00 x 1.10 x 1.10 = 93.2
Final estimate:
42-93+ days
Plain answer:
This is a long-tail case. The estimate is about 6-13+ weeks. This is not the average person, but it is possible for very heavy chronic use.
A short version of the calculator
Use this if you want a quick estimate:
- Estimate THC mg per day:
grams x 1000 x strength
- Find Dose Score:
THC mg per day / 50
- Multiply:
Dose Score x Frequency Factor x Duration Factor x Route Factor
- Match the score to the base range.
- Multiply the range by:
Body Factor x Activity Factor x Test Factor
- Round the answer to days.
Why this method is still uncertain
This method is better than saying “weed stays 30 days” for everyone. But it is still rough.
It cannot know:
- the true THC percent in the cannabis
- how deeply a person inhaled
- how much THC was really absorbed
- the person’s exact metabolism
- their real urine concentration
- the exact lab cutoff
- whether the first urine sample is before or after the metabolite peak
The estimate should be read like a weather forecast. It gives a likely range, not a promise.
Simple final guide
| User pattern | Simple estimate |
|---|---|
| One-time use | 1-4 days |
| Light occasional use | 2-7 days |
| Moderate repeated use | 5-14 days |
| Frequent use | 1-3 weeks |
| Daily use | 2-5 weeks |
| Heavy daily use | 4-8 weeks |
| Very heavy chronic use | 6-11+ weeks |
For a person who smoked medium-strength cannabis every day at about 1-2 grams per day, the calculator usually lands around 2-5 weeks if body type and activity are average. With higher body fat and a passive lifestyle, the estimate can move closer to 3-6 weeks. With years of heavy daily use, the long-tail range can be longer.
Sources
- Huestis MA, Mitchell JM, Cone EJ. “Urinary excretion profiles of 11-nor-9-carboxy-delta 9-tetrahydrocannabinol in humans after single smoked doses of marijuana.” Journal of Analytical Toxicology. 1996;20(6):441-452. DOI: 10.1093/jat/20.6.441. PubMed: 8889681.
- Goodwin RS, Darwin WD, Chiang CN, Shih M, Li SH, Huestis MA. “Urinary elimination of 11-nor-9-carboxy-delta9-tetrahydrocannabinol in cannabis users during continuously monitored abstinence.” Journal of Analytical Toxicology. 2008;32(8):562-569. DOI: 10.1093/jat/32.8.562. PubMed: 19007504.
- 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. DOI: 10.1038/clpt.1985.226. PubMed: 3902318.
- Smith-Kielland A, Skuterud B, Morland J. “Urinary excretion of 11-nor-9-carboxy-delta9-tetrahydrocannabinol and cannabinoids in frequent and infrequent drug users.” Journal of Analytical Toxicology. 1999;23(5):323-332. DOI: 10.1093/jat/23.5.323. PubMed: 10488918.
- Johansson E, Halldin MM. “Urinary excretion half-life of delta 1-tetrahydrocannabinol-7-oic acid in heavy marijuana users after smoking.” Journal of Analytical Toxicology. 1989;13(4):218-223. DOI: 10.1093/jat/13.4.218. PubMed: 2550702.
- Johansson E, Gillespie HK, Halldin MM. “Human urinary excretion profile after smoking and oral administration of [14C]delta 1-tetrahydrocannabinol.” Journal of Analytical Toxicology. 1990;14(3):176-180. DOI: 10.1093/jat/14.3.176. PubMed: 2165199.
- Schlienz NJ, Cone EJ, Herrmann ES, et al. “Pharmacokinetic Characterization of 11-nor-9-carboxy-delta9-tetrahydrocannabinol in Urine Following Acute Oral Cannabis Ingestion in Healthy Adults.” Journal of Analytical Toxicology. 2018;42(4):232-247. DOI: 10.1093/jat/bkx102. PubMed: 29300962.
- Spindle TR, Cone EJ, Schlienz NJ, et al. “Urinary Excretion Profile of 11-Nor-9-Carboxy-delta9-Tetrahydrocannabinol (THCCOOH) Following Smoked and Vaporized Cannabis Administration in Infrequent Cannabis Users.” Journal of Analytical Toxicology. 2020;44(1):1-14. DOI: 10.1093/jat/bkz038. PubMed: 31095692.
- Huestis MA, Blount BC, Milan DF, Newmeyer MN, Schroeder J, Smith ML. “Correlation of creatinine- and specific gravity-normalized free and glucuronidated urine cannabinoid concentrations following smoked, vaporized, and oral cannabis in frequent and occasional cannabis users.” Drug Testing and Analysis. 2019;11(7):968-975. DOI: 10.1002/dta.2576. PubMed: 30756523.
- Sempio C, Huestis MA, Kaplan B, Klawitter J, Christians U, Henthorn TK. “Urinary clearance of 11-nor-9-carboxy-delta-9-tetrahydrocannabinol: A detailed pharmacokinetic analysis.” Drug Testing and Analysis. 2022;14(8):1368-1376. DOI: 10.1002/dta.3259. PubMed: 35332698.
- Wong A, Montebello ME, Norberg MM, et al. “Exercise increases plasma THC concentrations in regular cannabis users.” Drug and Alcohol Dependence. 2013;133(2):763-767. DOI: 10.1016/j.drugalcdep.2013.07.031. PubMed: 24018317.
- Chayasirisobhon S. “Mechanisms of Action and Pharmacokinetics of Cannabis.” The Permanente Journal. 2020;25:1-3. DOI: 10.7812/TPP/19.200. PubMed: 33635755.
- Ewell TR, Abbotts KSS, Williams NNB, et al. “Pharmacokinetic Investigation of Commercially Available Edible Marijuana Products in Humans: Potential Influence of Body Composition and Influence on Glucose Control.” Pharmaceuticals. 2021;14(8):817. DOI: 10.3390/ph14080817. PubMed: 34451914.