The BRRRR strategy has been around for many years and stands for buy, repair, rent, refinance, and repeat. The reason the strategy has become so popular is that an investor can buy a rental property, and get most or all of their cash back out using a refinance. They can then use that money to buy another rental and repeat the process over and over again.
This calculator helps you figure out how much money you will spend or get back from the property after refinancing.
To learn more about the BRRRR strategy check out this in-depth article: How to use the BRRRR strategy to buy rentals with little money down.