That turned it into a +5. What is that actually doing?[/QUOTE
=19-SUM(T18:AO18,H18)
19:
The value you want your strength to be no matter what else you do. If you get a better magic item later, change this value to match the desired final Strength score.
SUM(T18:AO18,H18):
Finding the value of your existing strength. H18 is your starting ability score. T18:AO18 is the value for ASI gains at each level if you took any.
The formula didn't work because I left out Racial Modifiers. My bad.
Try this instead:
=19-SUM(N18:AO18,H18)