spread b/w cap rate and interest rate for cash flow

[Bay H.]

I learned about 50% rule and 2% rule here and their general use cases. I'm wondering whether there is any simple rule of thumb for cash flow generated from the spread between cap rate and interest rate.

For example, 1% rent/value ratio would give 6% cap rate after 50% rule. The formula for amortization is non-linear. Say if financed at 20% down and 5.5% 30yr fix, is any rule of thumb / empirical way to derive cash flow and COC quickly?