At first blush the answer sounds easy: if the year end total is in cell
A1, then the formula is =A1*1.03

However, since your budget is across several years, consider using the
POWER function. That will ensure the 3% increase is applied across all
years.
Year 1 formula: =A1*POWER(1.03,1)
Year 2 formula: =A1*POWER(1.03,2)
Year 3 formula: =A1*POWER(1.03,3)
etc.