Fairfield is in Solano County. Sproutly's list of local programs does not include Fairfield. The list is not complete, so Fairfield may still have its own rules. Check with the city before you raise the rent. Sproutly does not state local rules. You decide, from the official sources below.
The list of places is not complete. A city that is not listed may still have rules.
The calculator turns a percent into a new rent, or a new rent into a percent. It does not say what the limit is. The rent increase notice has you enter each legal value yourself, with a link to where to check it.