THC Calculator

What it is for and what it is not

After use, most people go by how they feel. But how you feel and what a test shows are two different things. The calculator gives you a number you can plan with: when it is reasonable to get behind the wheel and when to wait.

Why feeling fine is not enough

Everyone clears THC differently. It depends on how often you use, how much, in what form and how your metabolism works. One person is clear in a day, another carries it for weeks. So leave a margin. The result is a guide, not a line beyond which everything is fine.

What the calculator can and cannot do

• Estimates a rough level from what you enter. Instantly and for free.
• No sign-up needed. What you type stays in your browser.
• Does not replace a lab test, a doctor or a lawyer.
• The result is not a permission to drive.

Legal limit in the Czech Republic

In the Czech Republic the limit is 2 ng/ml of THC in blood serum under Government Regulation No. 41/2014 Coll. A roadside check starts with an indicative saliva test and is confirmed by a blood sample. Limits differ from country to country and the calculator cannot guarantee any of them, so do not drive after use.

How long is THC detectable

Indicative ranges from the scientific literature. The real time depends on frequency of use, dose, metabolism, body fat and test sensitivity. The calculator takes this into account, but still treat the result as an estimate.

• Urine: 1 to 3 days after a single use, 1 to 4 weeks with regular use, longer for long-term users.
• Blood: hours to 1 to 2 days, several days for regular users.
• Saliva: roughly 24 to 72 hours.
• Hair: up to 90 days.

For driving there is only one safe rule: do not drive after use.