two linked counters

i'm feeling a bit stupid to ask that but ok... i have a counter going up from 0-9. now i want to know the current number of this counter + 2 but without exceeding the range of the counter, that would mean:
counter 0 -> 2
counter 5 -> 7
counter 8 -> 0 (starting over)
counter 9 -> 1 (starting over)

i can get there with a second counter plus adding plus modulo plus five other boxes but this gets very convoluted (especially when the ranges of the counters change dynamically) and i'm pretty sure this can be solved much simpler - isn't there some simple cycle or round-robin for a number range?
k