Interest Rate Sensitivity Calculator
See how interest rate changes affect your monthly payment and total cost. Understand the impact of rate timing, points, and market movements.
Last updated October 18, 2026
How our math works
- 30-year fixed-rate loan of $360,000, fully amortizing; scenarios vary the interest rate around your 6.75% base
- Rates shown are interest rates used for estimation only — not APRs and not offers. APR reflects fees and other loan costs and may differ from the interest rate shown.
My scenario
Enter income, debts, price, and rate once. Every calculator pre-fills.
Loan Details
$
%
Your current or expected rate
Property Costs
%
$
Rate Lock Timing
Used to recommend locking vs. floating your rate
Payment at Base Rate
$2,335/mo
6.75% on $360,000 loan
$60/mo
$120/mo
$239/mo
$480,583
Over 30 yearsLock vs. Float
Should you lock this rate before closing?
Enter your expected closing date to see whether a standard 30–45 day lock covers you, or whether you should keep floating and lock later.
Rate Scenarios
How different rates affect your payment
5.75%
Monthly P&I
$2,101
Total Interest
$396,310
−$234/mo
6.25%
Monthly P&I
$2,217
Total Interest
$437,969
−$118/mo
6.50%
Monthly P&I
$2,275
Total Interest
$459,160
−$60/mo
6.75%
Monthly P&I
$2,335
Total Interest
$480,583
7.00%
Monthly P&I
$2,395
Total Interest
$502,232
+$60/mo
7.25%
Monthly P&I
$2,456
Total Interest
$524,100
+$121/mo
7.75%
Monthly P&I
$2,579
Total Interest
$568,470
+$244/mo
Payment Impact Visualization
See how rate changes affect monthly payment
5.75%
$2,101
6.25%
$2,217
6.50%
$2,275
6.75% (base)
$2,335
7.00%
$2,395
7.25%
$2,456
7.75%
$2,579
What This Means
Practical implications for your mortgage
Save $120/mo
$1,440/year
$2,335/mo
At 6.75%
+$120/mo
$1,440/year more
Key Insights
What these numbers mean for you
Base Rate
Base rate (6.75%): $2,335/month, $480,583 total interest
Rate Impact
±0.25%: Changes payment by ~$60/month
Rate Impact
±0.5%: Changes payment by ~$120/month
Rate Impact
±1.0%: Changes payment by ~$239/month
Insight
A 1% rate difference costs/saves $86,080 in interest over 30 years
Insight
Use this to decide: Is it worth paying points to buy down? Should you float or lock? How much does timing matter?
The Bottom Line
On a $360,000 loan, every 0.25% rate change affects your payment by $60/month($720/year). A 1% difference means $239/month more or less—that's $2,868/year and significant interest over 30 years.
Here are the exact formulas behind your numbers. No black boxes — just math.
Rate Sensitivity Math
Payment at Each Rate
Payment Change per 0.25%
Total Interest at Each Rate
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Frequently Asked Questions
Roughly 10% of the payment on a 30-year loan. On a $360,000 loan, moving from 6.75% to 7.75% raises principal and interest by about $245/month — around $88,000 over 30 years. This calculator charts your exact payment across a range of rates.
A rate lock protects you from increases between quote and closing, typically free for 30-45 days. If a rate rise would break your budget or approval, lock. Floating only pays off if rates fall during your escrow — a bet, not a plan. Enter your closing date on this page for a lock-versus-float recommendation.
A common trigger is about 0.75-1 point below your current rate, but the real test is break-even: closing costs divided by monthly savings, compared with how long you will keep the loan. Use the refinance calculator for the full analysis.