You can figure this out the same way as compound interest, but roughly for the years of increase you multiply it by;
First year - monthly pay x 1.25 = difference in monthly pay for year
Second year - monthly pay x 2.52
Third year - monthly pay x 3.8
Fourth year - monthly pay x 5.09
Fifth year - monthly pay x 6.41
...
anic: Warning! Math ahead!
new rate = current rate *(1+annual increase)^number of years gives you overall percent
example in year two = current rate * (1 + 0.0125) ^2
=current rate *1.0252 = new total monthly rate
pretty decent explanation here;
https://www.mathsisfun.com/money/compound-interest.html
Compound interest is crazy that way; an annual 1.25% increase gives you a 13% growth over 10 years. Or do 1.5% a month (18% year) for credit card interest and you can see how fast your debt grows.