If you have a fixed-rate mortgage, a rate rise won't change your principal and interest payment. That part of your payment is set for the life of the loan, no matter what happens to market rates. If rate headlines have you worried, check your loan type first. Most U.S. mortgages have a fixed rate: only about 4% of outstanding mortgages were adjustable in mid-2025.
A rate rise matters if you have an adjustable-rate mortgage (ARM) or a home equity line of credit (HELOC), or if you're about to buy or refinance. Here's how to estimate the change in each case.
How much each rate rise adds
On a 30-year fixed loan, each half-point increase adds about $32 to $35 a month for every $100,000 you borrow. A full point adds about $64 to $68.
| Rate | Monthly payment per $100,000 | Monthly payment on $400,000 |
|---|
| 5.5% | $568 | $2,271 |
| 6.0% | $600 | $2,398 |
| 6.5% | $632 | $2,528 |
| 7.0% | $665 | $2,661 |
| 7.5% | $699 | $2,797 |
| 8.0% | $734 | $2,935 |
These figures are principal and interest only. Property taxes, homeowners insurance, and mortgage insurance come on top.
So if rates move from 6.5% to 7% on a $400,000 loan, the payment goes from $2,528 to $2,661, or $133 more a month. Over a year, that's about $1,600.
Lenders use the same formula for every fixed-rate, fully amortizing loan:
M = P × r × (1 + r)^n ÷ ((1 + r)^n − 1)
M is the monthly principal and interest payment.
P is the loan amount.
r is the monthly interest rate: the annual rate divided by 12.
n is the number of monthly payments: 360 for a 30-year loan, 180 for a 15-year loan.
For $400,000 at 6.5% over 30 years:
r = 0.065 ÷ 12 = 0.0054167
(1 + r)^360 = 6.9918
M = 400,000 × 0.0054167 × 6.9918 ÷ (6.9918 − 1) = $2,528.27
Run it again with a new rate and subtract to see the change. The refinance calculator does this for you and also shows how the balance falls over time. For more on how each payment splits between principal and interest, see how amortization schedules work.
If you have an adjustable-rate mortgage
An ARM keeps its starting rate for a set period, often five, seven, or ten years. After that, the rate resets to an index plus a margin. Rate caps limit how far it can move.
The Consumer Financial Protection Bureau describes three caps:
Initial cap: how much the rate can change at the first reset, commonly 2 or 5 percentage points.
Periodic cap: how much it can change at each later reset, commonly 1 or 2 points.
Lifetime cap: how far it can ever rise above the starting rate, commonly 5 points.
Your loan documents list your caps, index, and margin. For most ARMs, your servicer must also send a notice 210 to 240 days before the first payment at the new rate is due, with an estimate of the new payment.
Here's how that plays out on a $400,000 loan with a 5.75% starting rate that resets every six months after year five, with 2/1/5 caps:
| Period | Rate | Monthly payment | Change from start |
|---|
| Years 1–5 | 5.75% | $2,334 | $0 |
| First reset (worst case) | 7.75% | $2,803 | +$468 |
| Second reset (worst case) | 8.75% | $3,047 | +$713 |
The rate can never go above 10.75%, the starting rate plus the 5-point lifetime cap.
The payment rises less than the rate alone would suggest, because by the first reset you've paid the balance down to about $371,000. The worst case isn't guaranteed. The new rate is the index plus the margin, limited by the caps. If that sum is lower, your payment rises less, and it can even fall.
If you have a HELOC
Most HELOCs have a variable rate, often tied to the prime rate, which moves when the Federal Reserve changes its target rate. The CFPB notes that HELOC payments may change from month to month. During the draw period, many HELOCs only require interest.
On a $50,000 balance, interest-only payments are about $333 a month at 8% and $375 at 9%. Check your statement for the rate, margin, and when the draw period ends. Payments are often much higher once the repayment period starts, because you begin paying principal.
Why your payment can rise on a fixed rate
A fixed rate locks the principal and interest, not your total payment. If you pay taxes and insurance through escrow, the total changes when those bills change. The CFPB lists higher property taxes or insurance premiums among the common reasons a mortgage payment goes up. Your annual escrow statement shows what changed.
What a rate rise means if you're thinking about refinancing
Rising rates don't affect a loan you already have at a fixed rate. They do shrink the gap between your rate and what lenders offer, which makes refinancing harder to justify.
If you have an ARM nearing its first reset, compare two numbers: your likely payment after the reset, and the payment on a fixed-rate refinance at today's rates, including closing costs. See how to convert an ARM to a fixed-rate mortgage for the steps. If rates are moving quickly while you shop, read when to lock your refinance rate.
To see whether a refinance pays off, enter your current loan and an offer in the refinance calculator. It shows the new payment, the break-even month, and the total cost while you keep the loan. The minimum rate calculator shows the highest rate at which a refinance still makes sense for you.
If refinancing doesn't work at today's rates, you can get alerts when it does.
