This is to prepare you for market fluctuations and look at how an investment would perform in a market crash scenario and test your ability to withstand vacancies, lower rents, or a decrease in home values.

Rates make be fixed for some time or may fluctuate from the start. 

Costs may fluctuate from month to month, and there's some margin of error that you need to account for.

I am using guaranteedrate.com they quoted me an interest rate of 3.625% and my credit score fluctuates between 780-800.

Obviously, that isn't a straight line correlation since comping is subjective and home values are always fluctuating.

Condo prices seem to fluctuate more and that's where I profited.I have better luck with small multi's and know the deficiencies of each when making the purchase, and plan accordingly.

Costs may fluctuate from month to month, and there's some margin of error that you need to account for.

Of course, that will fluctuate based on how cool or hot a tenant keeps the house.

The biggest cause of fluctuation in the bill is likely to be electricity usage, which will vary predominantly depending on how much a/c use there is (and heat if electric heat).

The garage conversion estimates can fluctuate dramatically depending on the site conditions.