Study the market.

@Albert Gallucci as many have pointed out, in the commercial space of 100+ apartment buildings and offices, property classes have some pretty decent industry standards.We started applying these to 1-4 unit properties around 10 years ago, which you can verify on our blogs, because we saw too many newbie investors not properly taking into account things like, neighborhood status, tenant pool, property condition, etc.Unfortunately, there's no industry standard for this, but you can use some basic logic to think your way through your own Classifications.

This means more cash in your account each month than if you pay a mortgage.

@Elizabeth KingYour accountant is wrong.

She took about two months studying outreach particular niche and instituted a program in steps where the results could be verified before implementing the next step.  

It took me 13 months to open a bank account in Belize.  

My duplex - built 1989, 2,060 sf, 2 bed/bath, 1 year old roof, value if I subdivide (county already approved) and sell each separately $150k each ($300k total)Investor duplex - built 1995, 2,300 sf, 2 bed/bath, 5 year old roof, value around $310kThe investors initial request was for an equal trade and they would pay realtor fees, which I replied wouldn't be equal due to buying/selling costs (recording fees, title insurance, closing fee, survey, inspections, loan fees, 1031 fees, accountant fees, repairs), taxes would increase due to new sale price, I'd trade a 3.75% mortgage for a higher one, and I'm on the 10th year of a 30 year loan so resetting that to a new loan would restart amortization and pay more towards interest.

4.5% is nice depending on how much you have in the account.

However I like to run my numbers conservatively and account for cap ex, vacancy, maintenance reserves 10/5-7/5-7% respectively.

If you don't have a great accountant which most are not.