A fire extinguisher needs to be inspected monthly so that you can count on it working properly. You want to be certain that it is ready to perform correctly in an emergency. A disposable fire extinguisher can only be used once, whereas one that is rechargeable can be used again after it is refilled. If your fire extinguisher is not full, then you'll need to get it recharged.
Check that pressure gauge on your fire extinguisher is in the green area.
Verify that the nozzle and locking pin are intact, the tamper seal is unbroken and the nameplate containing instructions is visible and in place on your fire extinguisher. Check the last service date, which should be within the past 12 months.
Check that your fire extinguisher is in good shape, without rust, dents or damage.