What are some helpful tools to crunch numbers on multi family?

[Brendan Chase]

Newbie here on the site. Stared listening to the podcast a few weeks back and am super excited about investing. I bought a duplex two years ago that nets about $250/month (although I should be raising the rent on one of the units....) I am currently excited about another duplex I stumbled upon that I think will work well for a brrrrr. Just curious if anyone has a favorite or best place/advice on crunching numbers to make sure everything works. Thanks for the help!