THC Calculator

By: Patrick Myers Patrick Myers is the CEO and Founder of Calculator Academy. He has over eight years of experience developing online calculators and holds a B.S. in Mechanical Engineering. His work focuses on formula implementation, calculator accuracy, unit conversions, and creating practical tools that are easy to use.

Last Updated: October 7, 2026

Calculate calendar days since last cannabis use and read test-specific limitations. This tool does not predict a clean date or a drug-test pass probability.

Count calendar days between two dates. Dates, body weight and self-rated metabolism cannot establish a personal clean date or drug-test pass probability.

Enter the calendar date of last use. This tool does not assess impairment.

Use a date on or after last use. The default is your device’s current date.

This selects an explanation, not a multiplier or pass prediction.

Settings

How long will THC stay in my body? 

The calculator counts dates; it does not forecast clearance. Mayo Clinic Laboratories lists these approximate urine examples at a 3 ng/mL quantitation limit:

  • Single use: approximately up to 3 days
  • Moderate use (4 times weekly): approximately up to 5 days
  • Heavy daily use: approximately up to 10 days
  • Chronic heavy use: approximately up to 30 days

These examples depend on dose, use history and metabolism. They are not an individual deadline, a guarantee, or the cutoff used by every test.

What can a THC drug test tell me?

A calculator cannot determine whether a particular sample will be positive. Body weight, amount used, self-rated metabolism and dates do not establish a personal pass probability.

The revised result is calendar arithmetic: comparison date minus last-use date. It excludes the starting date; matching dates give zero days.

For example, October 1 to October 11 is 10 calendar days. This result does not establish a negative test or lack of impairment.

Consult the laboratory or medical review officer about the actual test and cutoff. Calendar time alone cannot resolve the result.

Changes in fluid intake, diet or exercise do not establish a predictable negative test result.

Use the actual test result and appropriate professional interpretation when a decision depends on the result.

THC Blood Tests and Hair Tests

ARUP Laboratories distinguishes specimen types and assay methods. Detection is affected by the analyte, test design and specimen quality.

Blood and oral fluid usually concern more recent exposure than urine. There is no reliable universal blood window that applies regardless of use history.

Hair can reflect exposure over a longer history. Segment length and laboratory method matter; a urine window cannot simply be doubled to predict a hair result.

A urine result alone does not establish impairment, dose or the exact time of use. Screening results may require confirmation and clinical interpretation.

THC VS CBD 

THC produces cannabis intoxication. CBD is a different compound; products sold as CBD may contain THC or interact with some assays, so a negative THC test is not assured.

The FDA warns that unapproved CBD products have not been evaluated for their claimed benefits or safety. Discuss use with a healthcare professional.

Calculator Changelog:

  • October 7, 2026: replaced unsupported clean-date and pass-percentage estimates with exact calendar-day counting; retained explanations for urine, hair, oral fluid and blood testing.
THC Calculator screenshot