The withholding can also be stopped altogether, and only actual taxes owed will be collected by filing form MW506NRS at least 21 days prior to settlement and filing it with the Comptroller of Marylands office to get the exact actual tax owed calculated. 

Here's a bit more in detail about how rates are calculated for DSCR loans:1.

From the looks of it this thing is no worse than the BP Calculator.

@Daniel Na https://www.wikihow.com/Calculate-Compound-Interest

@Dav idWithout going through the numbers again, my guess is your calculation goes astray at the calculation of the Heloc costs.

The property itself should bring in revenue ( even if you choose not to live in one side) and generally a bank will accept a portion of that rental income into the calculation. 

Remaining Balance: After the balloon payment, the remaining loan balance will be re-amortized over 5 years (60 months) at the same 6.5% interest rate.Payment TermsInitial Loan Terms (First 24 Months):The monthly payment for the first 24 months is based on a 12-year amortization schedule:Monthly Payment for First 24 Months: $1,573.39Remaining Balance at Month 24 (Prior to Balloon Payment):The balance after 24 months can be calculated using the amortization formula:Remaining Balance at Month 24: $157,113.92Balloon Payment:The balloon payment will be 50% of the remaining balance at Month 24:Balloon Payment Due at Month 24: $78,556.96Re-Amortization of Remaining Balance (After Balloon Payment):The remaining balance after the balloon payment will be:This amount will be re-amortized over 5 years (60 months) at the same 6.5% interest rate.Monthly Payment for Final 60 Months: $1,541.18Summary of Key Terms:• Purchase Price: $215,000• Down Payment: $43,000• Loan Amount: $172,000• Interest Rate: 6.5% (fixed)Initial Terms (First 24 Months):• Monthly Payment: $1,573.39• Balloon Payment Due at Month 24: $78,556.96Re-Amortized Terms (Final 60 Months):• Remaining Balance: $78,556.96• Monthly Payment: $1,541.18Additional Conditions:1.

Quote from @Erick Pena: A "good" rental property is one that covers all expenses (mortgage, taxes, insurance, maintenance, property management fees, and any other costs) and still leave a surplus (commonly referred to as cash flow).Calculate cash flow as: Cash Flow = Rental Income − Operating Expenses − DebtThere's much more to it, but that's the basic idea.

How do you calculate rehab cost given you can’t look inside? 

Helocs have many different ways to calculate income once you get outside of the bank world.