How long does methotrexate stays in your body for?

Variable: Different people metabolize Methotrexate at different rates. Some very sensitive people notice one missed dose, and at the other extreme some can go a month or more before the effect is lost. If the concern is over a desire for preganancy (not allowed on methotrexate), a washout period of 3 months is often suggested.

3-4 weeks: That is difficult to answer. The half life of Methotrexate is only 15 hours but it remains in the liver longer. I would say it would be gone in 3 weeks or so.