There are formulas and guidelines that can help you figure out what your financial goals are for your investment. 

Then learn how to live on the left side of the "=" in the formulas, instead of the right side...where most REI live.

Our formula is like @Mike Hartzog  all accrual  as we are just short term gap and bridge.. in the few instances that we do get payments we just book it to quick books.. 

I found that the IRR formula was exceedingly complicated and while I could use a computer to find IRR, I dislike following methods I can't understand.

Also is effective the "yield"Formula: Net Operating Income (NOI) / Value = Cap RateAlternatively: NOI / Cap Rate = ValueExample$100,000 NOI$1,000,000 ValueCap Rate = 10% ($100,000 / $1,000,000)This million dollar property has a cap rate or "yields" 10% annual returns in the form of a $100,000 net operating income.

@Wayne Brooks - Is there a formula or table somewhere to figure out the percentage of principal remaining at certain periods of amortization?

Opendoor is active in Phoenix but it looks like they haven't figured out a formula yet.They bought this property Oct 31 2018 for $245,700 and after 228 DOM are asking $249,000 - who knows how much they put into the rehab and what their carrying costs are but seems to me that putting the money into hotdogs and selling them at the beach would have a better return. 

No secret formulas or magic in REI.

Research investor formulas on BP. 

“Overcome fear”“Make your money work for you”“Learn a new formula ““Learn a new skill”Are a few principles from RDPD and I am glad I applied them. #3 is coming and I will be ready to ride that wave up.