i am a fairly basic user of Excel and i am looking for some help with a formula

i have just started a new job as a maintainance planner

what i need to do is predict serviceing of machines over the next year

the first service is sorted using these formulas
if the current hours vs the next service fall with in these values Due appears in the box under the date this will predict the first service

=IF(C7<=24,"DUE","")
=IF(AND(C7>=24,C7<=48),"DUE"
=IF(AND(C7>=48,C7<=72),"DUE",""
and so on

what i need is to predict future services over a time line

services are due in intervels of 250hrs

i hope this is clear any help would be appreciated

Regards