Calculator Documentation
Portfolio DSCR Calculator
Blended DSCR across your rental portfolio and how much more you can borrow
Schema version 1.0.0 · Category: investment
Inputs
Current Portfolio (Totals)
Combined monthly figures across all properties
| Field | Type | Default | Notes |
|---|---|---|---|
| Total Monthly Rent | currency | $12,000 | Gross rent across every property |
| Total Monthly P&I | currency | $6,500 | All existing mortgage payments combined |
| Total Monthly Taxes | currency | $1,500 | Property taxes across the portfolio |
| Total Monthly Insurance | currency | $600 | Insurance across the portfolio |
| Total Monthly HOA | currency | $0 | HOA dues across the portfolio |
New Loan (Optional)
A loan you are considering adding
| Field | Type | Default | Notes |
|---|---|---|---|
| New Loan Amount | currency | $0 | Set to 0 if just checking the current portfolio |
| New Loan Rate | percentage | 7.50% | Rate on the prospective loan |
| New Loan Term (Years) | number | 30 | Term of the prospective loan |
| New Property Monthly Rent | currency | $0 | Rent the new property adds (0 for a cash-out on existing) |
| New Property Taxes+Ins/mo | currency | $0 | Monthly taxes and insurance the new property adds |
Lender Requirement
The ratio to underwrite against
| Field | Type | Default | Notes |
|---|---|---|---|
| Required DSCR | number | 1.2 | Portfolio/blanket lenders typically require 1.15-1.25 |
Calculations
Every figure this calculator produces, in evaluation order. Formulas reference input ids, parameters, and earlier calculations.
currentPITIACurrent portfolio PITIA
totalMonthlyDebtService + totalMonthlyTaxes + totalMonthlyInsurance + totalMonthlyHOA
currentDSCRBlended DSCR today
totalMonthlyRent / max(currentPITIA, 1)
newMonthlyRateNew loan monthly rate
newLoanRate / 12
newTermMonthsNew loan months
newLoanTermYears * 12
newLoanPaymentP&I on the prospective loan (0 when amount is 0)
(newLoanAmount * newMonthlyRate * pow(1 + newMonthlyRate, newTermMonths)) / (pow(1 + newMonthlyRate, newTermMonths) - 1)
proFormaPITIAPITIA with the new loan
currentPITIA + newLoanPayment + newPropertyCosts
proFormaRentRent with the new property
totalMonthlyRent + newPropertyRent
proFormaDSCRBlended DSCR after the new loan
proFormaRent / max(proFormaPITIA, 1)
maxAdditionalPaymentRoom left in the portfolio for new debt service
max(proFormaRent / requiredDSCR - currentPITIA - newPropertyCosts, 0)
maxAdditionalLoanMaximum additional borrowing at the required DSCR
(maxAdditionalPayment * (pow(1 + newMonthlyRate, newTermMonths) - 1)) / (newMonthlyRate * pow(1 + newMonthlyRate, newTermMonths))
proFormaShortfallFlag: 0 = portfolio meets the required DSCR with the new loan
if(proFormaDSCR < requiredDSCR, 1, 0)
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