Interest Rate Impact Calculator
See how a small rate change affects your monthly payment and lifetime interest. On a $300k 30-year mortgage, +1% adds about $192/month and $69k lifetime.
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How to use
- 1 Enter loan principal (mortgage balance, auto loan amount, etc.).
- 2 Enter current/quoted APR (mortgage typically 6.30%, auto 7-10%, personal 10-15%).
- 3 Enter loan term in months (360 = 30-year, 180 = 15-year, 60 = 5-year auto).
- 4 Click Calculate to see scenarios at -1%, current, +1%, +2% — total interest and monthly payment for each.
- 5 Use to: stress-test ARM exposure, validate refinance benefits, compare lender rate quotes, model future rate environments. The +1% scenario is most useful for typical sensitivity.
About Interest Rate Impact Calculator
FAQ
Q How much does 1% rate change affect my mortgage?
On a 30-year $300,000 mortgage at 6.30%, a 1 percentage point increase to 7.30% adds approximately $67,000 in total interest over the loan life and increases monthly payment by ~$200. Higher principal = bigger impact.
Q What is the current 30-year mortgage rate?
Freddie Mac PMMS 30-year fixed at 6.30% (April 2026, 6.37% May 2026). Down from 7.79% peak Oct 2023. Most economists expect 5.75-6.50% range through 2026 absent major Fed policy changes.
Q What is the Fed Funds rate in 2026?
Federal Reserve held federal funds rate at 4.25-4.50% through Q1 2026. Markets pricing in 1-2 cuts in H2 2026 if inflation stays below 2.5%. Each Fed cut typically translates to ~0.25-0.50% mortgage rate movement.
Q What is rate shock for ARM borrowers?
When ARM teaser rate ends and fully-indexed rate kicks in. Example: 5/1 ARM at 5% can adjust to 7% (annual cap +2%) then 9% next year then capped at 10% (lifetime cap +5%). Monthly payment can DOUBLE. CFPB requires lenders to qualify borrowers at fully-indexed rate.
Q How does the Fed affect mortgage rates?
INDIRECTLY. Fed sets short-term rate (federal funds). Mortgage rates follow 10-Year Treasury yields, which are influenced by Fed expectations + inflation outlook. Plus MBS spread (~1.5-2.5%). Result: 30-yr mortgage = roughly 10-yr Treasury + 1.5-2.5%.
Q Should I wait for rates to drop?
Hard to time. Mortgage rates have been 5.75-7.79% range last 2 years. Each month waiting at higher rate costs $200-$400. If rates drop later, REFINANCE — but if rates rise, you're stuck. Better: buy when affordable + good home; refinance opportunistically.
Q How is APR different from interest rate?
INTEREST RATE: cost of borrowing money. APR: includes interest + lender fees + points + most upfront costs. APR is usually higher than rate. Use APR for accurate lender comparisons. CFPB Loan Estimate shows both.
Q What is "buying down" the rate?
Paying upfront points (1 point = 1% of loan) for a lower rate. Typical: 1 point reduces rate by 0.25%. Math: $300K loan, $3,000 point cost, saves $50/mo = 60-month break-even. Worth it if you'll stay 5+ years and have cash.
Official resources
Federal Reserve — Federal Funds Rate
Federal Reserve official federal funds target rate history and current level — drives all interest rates.
FRED — 10-Year Treasury Constant Maturity Rate
St. Louis Fed daily 10-Year Treasury yield — primary driver of 30-year mortgage rates.
Freddie Mac PMMS — Weekly Mortgage Rates
Weekly Freddie Mac Primary Mortgage Market Survey for current 30-year and 15-year rates.
CFPB — Adjustable-Rate Mortgages
Consumer Financial Protection Bureau guide to ARM rate caps, payment shock, and qualifying.