I would like to find an Excel sheet calculator to use with my hard money cash provider to review the metrics of a deal and something we can both contribute to reviewing the calculations and terms.

You also have to realize that even if you are not using the entire heloc limit "Some" underwriters still calculate the Maximum payment into consideration.There are some ways to pull money out of a Heloc and deposit it into a savings/checking account prior to application to satisfy the PITI reserve requirements.

Your time is worth more than the time it takes to calculate the interest. 

I have found a number of other users posted this question in the forum over the years but I cannot find a resolution anywhere.The way the Rental Property Calculator derives the "Profit if sold" number seems to have an error in it if you are using the function to increase the rental rate and expenses each year.

Here're some online calculators: from Intuit/TurboTax, from H&R Block, from NerdWallet, from TaxAct, and you can find dozens more online.

Note they will cost around 35-40/mo so make sure you calculate that as part of what you actually earn as that is a seller expense (if it’s gonna be owner occupied property) - if it’s not then you could charge it to borrower

Here, you'll get acclimated with market rents in your areas of interest.If you sign up for a PRO membership here on BP, you'll have access to multiple calculators to help you analyze deals.

Just make sure you don't over pay… That's a math calculation. 

Pros get:Unlimited analysis calculator reports, rental price estimates, and rehab estimatesAccess to discounted educational bootcamps ($225 per course for Pro members only)Free property management software from RentRediFree off-market deal finding tool from InveloAccess to the pro-only forum in our community Access to exclusive pro-only video content like workshops and webinar recordingsLawyer approved lease agreement forms for all 50 states – $99 value per stateIf you are sure you want to cancel before the auto renewal, you will lose access to this exclusive content!

Sign up for BPPro to get access to the Rental Calculator where you can analyze as many rental deals as you possibly can and plan to analyze 100 deals a week until you’ve found the perfect one to buy.