The starting amount is 100% of itself, so an increase uses a multiplier bigger than 1 and a decrease uses a multiplier smaller than 1. For example, a 6% increase uses $1.06$, while a 6% decrease uses $0.94$.

To build a multiplier, rewrite the new percentage as a decimal. So 8% increase means $108\%=1.08$, and 25% decrease means $75\%=0.75$. Compound interest and depreciation both use these multipliers again and again over time.