For the most part, it is three years for Federal income tax returns (States vary) and four years for payroll.

However, it is interesting that "three years" isn't what you may expect, and could be closer to four years.  Below is an excerpt of an article that mentions the weird timing, as well as some other interesting information about how long we need to keep records (and some thoughts about keeping them longer).

"The return copies or the list must be maintained for three years after the close of the return period (as defined in Sec. 6060(c)). Unfortunately, the term “return period” as defined for this section is most likely not the period that most practitioners would anticipate. Rather, it is the 12-month period beginning on July 1 of each year and is unrelated to the tax return period or the tax return deadline.

For example, a tax preparer prepares and delivers an individual 2022 return in August 2023. The “return period” per the Sec. 6060(c) definition ends on June 30, 2024, so a copy of the return (or the list) would need to be maintained until June 30, 2027."

https://www.thetaxadviser.com/issues/2023/feb/documentation-and-recordkeeping-for-tax-practitioners....