Formula for every 200hrs cycle

Hello,

now i'm trying to do a schedule maintenance for one part.the hours for the parts will increase everyday.e.g today 240 hrs,tomorrow 256 hrs.so,let say the hours due for inspection is 400hrs.so I want it to indicates how many hours left.that mean 144 hours,but i want it to countinously did the same thing on the next cycle.e.g 412 hours.hours due on 400 hours and the formula indicates 188 hours.Please help me.