Multiply the current rent by the percent and divide by 100. Add that to the rent. $2,000 at 5% becomes $2,100. The increase is $100 a month, which is $1,200 over twelve payments.
A notice that names a new dollar rent does not need this page: subtract the old rent from the new one. A local limit on how large a percent may be is the rule in that place, and this page does not look it up.