rule of thumb for starting out numbers. Help needed.

[Andrew Butler]

Hello Everyone! 

I'm a beginner here just slowly learning so i don't ruin my life on my first deal, so thank you all in advance. My question has to do with running the numbers to valuate a potentially "good deal"

I've been reading about the 50% rule which makes great sense as a guideline. My question is about a downpayment, and how that should be factored into the numbers. i.e. if you only put 3.5% down and are cash flowing after the 50% rule that seems like a good deal to take a closer look at. But what if someone wants to avoid PMI and put 20% down? or possibly more? what % of cash flow would you suggest is a decent amount on the principle?

Say i find a single family home for $300,000 and put $60,000 down (20%). As a rule of thumb what is the cash flow % on your equity should you expect if you're following the 50% rule?

Thanks,

Andrew