The only way you'll know if your car hits the mile mark is by having a functioning odometer. But the plastic gears that turn an analog odometer have a tendency to break, which causes the odometer to stop spinning. The good news is that this is an easy fix, as .
If both your odometer and speedometer are not working, then it's likely your speed sensor needs to be replaced. These are easily installed and located near the back of your transmission. If only your odometer is busted, then it's likely the gears that turn the odometer have broken. You need to pull instrument cluster to get at those gears, but it's not too bad to repair so long as you know what you're doing.
Since you've got your cluster out, make sure you remove any dust using compressed air and clean the clear plastic using a microfiber cloth. It's also a great time to upgrade your cluster lighting and throw in a couple of LEDs. That way your car will give out long before the odometer gives you any more trouble.