As an estimate, after taking a dose of Flexeril it should be out of your system within 5.5 days to 16.5 days.

Flexeril has a long half life of between 1 and 3 days. This is the time it takes for your body to reduce the plasma drug levels by half. Flexeril is eliminated slowly from the body. It usually takes around 5.5 x half-life for a drug to be eliminated from your system. This is (5.5 x 1) 5.5 days to (5.5 x 3) 16.5 days for Flexeril.

However other factors to consider include:
1. How much and how often you have taken the drug.
2. Your metabolic rate – a slower metabolism will increase the time a drug remains in your system.
3. Your age and health – older age and poor health will generally increase the time the drug stays in your system.
4. Body mass – generally the bigger you are the longer a drug will remain in your system.