How Interest Rates Change a Rental Deal
A single point of rate moves cash flow more than most investors expect — and it moves DSCR faster still.
7.43%
The rate at which this deal's cash flow reaches exactly zero.
The sensitivity, on one deal
The $240,000 example: $2,100 rent, NOI $15,004, $180,000 loan over 30 years, $67,200 of cash invested. Only the rate changes.
| Rate | Monthly P&I | Annual cash flow | DSCR | Cash-on-cash |
|---|---|---|---|---|
| 5.00% | $966 | $3,408 | 1.29 | 5.1% |
| 6.00% | $1,079 | $2,054 | 1.16 | 3.1% |
| 6.75% | $1,167 | $995 | 1.07 | 1.5% |
| 7.50% | $1,259 | −$99 | 0.99 | −0.1% |
| 8.00% | $1,321 | −$846 | 0.95 | −1.3% |
Three percentage points of rate — 5.00% to 8.00% — swing annual cash flow by $4,254, from comfortably positive to clearly negative. The property did not change. The rent did not change. The tenant did not change.
Why rate moves feel disproportionate
Two rates worth calculating for every deal
For the $240,000 example
- Break-even rate — where cash flow hits zero
- ≈ 7.43%
- Rate needed for a 1.25 DSCR
- ≈ 5.31%
- Rate actually available
- 6.75%
The deal is 0.68 points from break-even and 1.44 points from being genuinely safe.
These two numbers tell you more than any rate forecast. The first says how much room you have. The second says what environment this property was priced for — and when the answer is “an environment that does not currently exist”, you have learned something about the asking price rather than about interest rates.
What actually moves when rates move
| Effect | Speed | Direction |
|---|---|---|
| Your payment (on a new or adjustable loan) | Immediate | Up. Roughly $115/month per point per $180,000 borrowed. |
| DSCR | Immediate | Down, and faster than cash flow in percentage terms. |
| The maximum loan a lender will write | Immediate | Down — if the lender sizes to a DSCR floor, a higher rate means a smaller loan and more cash needed. |
| Cap rates in the market | 6 – 24 months, imperfectly | Up, eventually. Sellers resist, transaction volume falls first, prices follow later. |
| Rents | Slow, indirect | Often up — higher rates price buyers out of ownership and into renting. This is the one effect that works in your favour. |
| Your existing fixed-rate payment | Never | Unchanged. This is the whole value of fixed-rate debt. |
That last row is worth dwelling on. A 30-year fixed loan is an unusual instrument: you keep the low rate if rates rise, and you can refinance if they fall. The optionality is real and mostly free — which is a strong argument against interest-only and adjustable structures unless you have a specific reason.
Levers when the rate is too high
| Lever | What it does | The catch |
|---|---|---|
| Larger down payment | Smaller loan, lower payment, higher DSCR. | Lowers your return if the deal is already in negative leverage. See the down-payment ladder. |
| Buy points | Permanently lower rate. | Break-even is often 4–7 years. Only worth it if you are certain of the hold. |
| Seller-paid rate buydown | Same effect, seller’s money. | Temporary buydowns (2-1) expire — model the fully-indexed payment, not year one. |
| Longer amortisation (40-year) | Lower payment, better DSCR. | Far more total interest and much slower equity build. |
| Interest-only period | Lowest payment during the period. | No amortisation, and a payment shock at reset. Model the reset. |
| Negotiate the price | Directly raises cap rate against a fixed constant. | The only lever that improves the deal rather than the financing. |
That last row is the honest one. Rates are a market condition; price is a negotiation. On this deal, a $20,000 price reduction raises the cap rate from 6.25% to 6.82% and adds roughly $1,100 a year of cash flow — more than a full point of rate, and it does not expire.
“Marry the house, date the rate” — with a caveat
The practical move is to run the ladder on your own deal before you make an offer. The free calculator recomputes cash flow, DSCR and cash-on-cash live as you move the rate, so finding your break-even is a matter of dragging a number until cash flow hits zero.
Frequently asked questions
How much does a 1% interest rate increase affect rental cash flow?
On a $180,000 30-year loan, one percentage point adds roughly $110 to $125 a month depending on the starting rate — about $1,300 to $1,500 a year. Because cash flow is a small residual between two large numbers, that is frequently more than the entire annual cash flow of a market-priced deal.
What is a break-even interest rate?
The rate at which annual debt service exactly equals NOI, leaving zero cash flow. Calculating it for each deal tells you how much rate headroom you have, which is far more actionable than trying to forecast where rates will go.
Do higher interest rates lower property prices?
Eventually and imperfectly. Higher rates raise required cap rates, which implies lower prices for the same NOI, but sellers resist and transaction volume tends to fall before prices adjust. The lag can run well over a year, which is why rate increases hit cash flow long before they show up as buying opportunities.
Should I buy points to lower my rate on a rental?
Compare the upfront cost against the monthly saving to find the break-even month, typically somewhere between four and seven years. Points make sense for a long, certain hold and are usually a poor trade if you may sell or refinance sooner — and they also increase your cash invested, which lowers cash-on-cash return.