The "70% Rule" is a purchase criteria commonly used by real estate investors when analyzing properties that require rehab work, especially house flips and BRRRRs.

According to this rule, the purchase price of a property you're buying should be less than or equal to 70% of its after repair value (or an adjusted multiple), minus the rehab costs you expect to have.

If the 70% after repair value multiple is not accurate for your specific market, you can adjust it to better match your targets.