Rental Cash Damming Calculator
Models the cash-damming flow on your numbers: rental net cash flow redirected to the personal mortgage, rental operating expenses charged to a HELOC, deductible interest claimed annually, refunds reinvested. The headline number is years off the personal mortgage.
Years off the personal mortgage
6.2 years
Paid off in 18.8 vs 25 years without the strategy.
Net wealth improvement
$1,964,412
Over 30 years, including FV of invested payment savings and rental value at horizon.
Debt conversion
18.8 yrs
Total tax refunds
$102,863
Future payments saved
$204,234
Pre-tax income equivalent
$340,390
At year 30 (wealth horizon)
| Future value of invested payment savings | $896,187 |
| Future value of rental | $1,274,313 |
| Rental mortgage remaining | ($0) |
| ILOC balance (deductible debt) | ($206,087) |
Personal mortgage paydown
Balance over time, with cash damming vs without. The HELOC line shows deductible debt growing in the background.
Net rental cash flow, 5-year bands
Average monthly net rental cash flow per band, with rent appreciation applied. Negative numbers are the dam volume.
| Window | Avg monthly net cash flow |
|---|---|
| Year 1 to 5 | +$52.21 |
| Year 6 to 10 | +$292.16 |
| Year 11 to 15 | +$557.08 |
| Year 16 to 20 | +$849.57 |
| Year 21 to 25 | +$1,172.51 |
| Year 26 to 30 | +$1,529.06 |
Personal monthly payment
$2,759.92
ILOC ceiling (today)
$205,000
Capacity grows as the personal mortgage shrinks.
Recommended clearing-account buffer
$728
~1.5 months of rental true cost.
Things to know on these inputs
- ILOC capacity ceiling reached during the simulation. The strategy can't fully run at this scale; consider higher home value, lower starting mortgage balance, or shorter horizon.
What this is actually doing
Each month, rental income flows to the personal mortgage as additional principal. Operating expenses on the rental are paid from a HELOC instead. The HELOC interest is tax-deductible against rental income. Once a year, the tax refund flows back at the personal mortgage. Repeat for the amortization. Net effect: non-deductible personal-mortgage interest is slowly converted into deductible HELOC interest while accelerating the personal-mortgage payoff.
This is an estimated outcome. Real results depend on discipline, lender cooperation, and CRA documentation. Implementation belongs with a qualified CPA who can review your T776 history and confirm the structure on your file.
What this calculator misses
Cash damming lives or dies on tracing. The model assumes every HELOC dollar is used for the rental operating expense it's tagged for, every personal mortgage prepayment comes from rental net cash flow, and the accounts never co-mingle. In practice, even one personal expense run through the rental HELOC can contaminate the deduction. The calculator can't enforce discipline. The strategy call is where the implementation plan gets built.