What This Calculator Does
An interest-only mortgage lets you pay only the interest on the loan for an initial period, typically 5, 7, or 10 years. During this time, your monthly payment is lower because no principal is being repaid. After the interest-only period ends, the loan converts to a fully amortizing loan: the entire principal must be repaid over the remaining term, which causes a significant payment increase known as "payment shock."
This calculator shows your monthly payment during the interest-only period, the payment after it ends, the payment shock, and the extra interest you pay compared to a fully amortizing loan from day one. It also compares the total interest cost of both approaches. For a standard fully amortizing mortgage, use our Mortgage Calculator. For jumbo interest-only loans, see our Jumbo Loan Calculator.
Current Interest-Only Rates (2026)
Interest-only mortgages are typically structured as adjustable-rate mortgages (ARMs). As of mid-2026, IO rates range from approximately 5.75% to 6.50% depending on the ARM structure. A 5/1 ARM IO starts around 5.75% to 6.00%, a 7/1 ARM IO around 5.875% to 6.125%, and a 10/6 ARM IO around 6.125% to 6.50%. These rates run about 0.25% to 0.50% higher than comparable fully amortizing ARMs because lenders view interest-only loans as riskier. Some lenders also offer fixed-rate IO loans, typically at rates similar to or slightly above the 30-year fixed conforming rate of 6.71% (Freddie Mac, September 3, 2026).
Inputs Required
- Loan Amount: The principal you are borrowing. IO loans are common for jumbo loan amounts.
- Interest Rate: The rate during the IO period. For ARMs, this is the initial fixed rate.
- Interest-Only Period: 5, 7, or 10 years. During this time, you pay only interest.
- Total Loan Term: 30 or 40 years. After the IO period, the principal is amortized over the remaining years.
- Property Tax and Insurance: Monthly estimates for your area, added to both the IO and amortizing payments.
Outputs Provided
- IO Monthly Payment: Your payment during the interest-only period (interest plus tax and insurance).
- Amortizing Monthly Payment: Your payment after the IO period ends, when principal repayment begins.
- Payment Shock: The dollar and percentage increase when the IO period ends.
- Total Interest (IO Period): All interest paid during the IO years, with no principal reduction.
- Extra Interest Cost: The additional interest you pay compared to a fully amortizing loan for the full term.
How the Calculation Works
The interest-only payment is the simplest mortgage calculation:
IO Monthly Payment = Loan Amount x (Annual Rate / 12)
Amortizing Payment = P x [r(1+r)^n] / [(1+r)^n - 1]
Where n = (Total Term - IO Period) x 12 months
During the IO period, you pay only interest, so the principal balance never decreases. When the IO period ends, the full principal must be repaid over the remaining term. If you have a 30-year loan with a 10-year IO period, the principal is amortized over just 20 years instead of 30. This compressed repayment schedule is what causes the payment shock.
On a $600,000 loan at 6.25% with a 10-year IO period on a 30-year term, the IO payment is $3,125/month. After year 10, the $600,000 must be amortized over 20 years at the same rate, producing a payment of $4,395/month. The payment shock is $1,270, a 41% increase. The total interest over the life of the loan is $749,900, compared to $729,900 for a fully amortizing 30-year loan at the same rate. The extra interest cost is $20,000 because no principal was paid during the first 10 years.
How to Use the Calculator
- Enter your loan amount. Interest-only loans are most common for jumbo loan amounts above $832,750.
- Set the interest rate. For ARMs, use the initial fixed rate. For fixed-rate IO loans, use the quoted rate.
- Choose your interest-only period (5, 7, or 10 years).
- Select the total loan term (30 or 40 years).
- Add your monthly property tax and insurance estimates.
- Review the IO payment, the post-IO payment, and the payment shock.
- Compare the extra interest cost against the benefit of lower early payments.
Example Calculations
Example 1: Jumbo IO with 10-Year Period
Alex, a physician in Boston, finances a $1,200,000 home with a $960,000 jumbo IO loan at 6.25% with a 10-year IO period on a 30-year term:
- IO monthly payment: $5,000 (interest only)
- Total interest during IO period: $600,000 (10 years x $60,000/yr)
- Amortizing payment (years 11-30): $7,032 (amortized over 20 years)
- Payment shock: $2,032/month (41% increase)
- Total interest over 30 years: $1,199,680
- Full amortizing 30-year payment at 6.25%: $5,923
- Full amortizing total interest: $1,172,280
- Extra interest cost of IO: $27,400
Alex saves $923/month during the first 10 years ($110,760 total), but pays $27,400 more in total interest over the life of the loan. He plans to sell the home within 10 years, so the extra lifetime interest is irrelevant to him. The IO loan gives him lower payments during his high-earning but debt-heavy early career years. If he stays beyond year 10, the payment jumps to $7,032, which he needs to be prepared for.
Example 2: 7/1 ARM IO with Rate Adjustment
Maria finances $500,000 with a 7/1 ARM IO at 5.875% with a 7-year IO period on a 30-year term. During years 1-7, she pays $2,448/month (interest only). After year 7, the rate adjusts. If the rate stays at 5.875%, her amortizing payment over 23 years is $3,323/month, a shock of $875 (36%). If the rate adjusts up to 7.5%, her payment becomes $4,094/month, a shock of $1,646 (67%). Maria uses this calculator with both rate scenarios to stress-test her budget. She also models a refinance into a fixed-rate loan at year 5 using our Refinance Calculator.
Real-World Scenarios
High-Income Professional with Expected Income Growth
Dr. Patel is a surgical resident earning $65,000/year, with a guaranteed salary jump to $450,000+ in 5 years when she finishes training. She buys a $900,000 home with a 10-year IO loan at 6.25%. Her IO payment of $4,688/month is manageable on her current income with her husband's $80,000 salary. By year 10, her income will be well over $500,000, making the $6,575 amortizing payment affordable. The IO loan matches her payment schedule to her income trajectory. Without the IO feature, the fully amortizing payment of $5,523/month would strain their current budget. This is the textbook use case for interest-only mortgages.
Investor Using IO for Cash Flow
Michael buys a $1.5 million rental property with a 25% down payment, financing $1,125,000 with a 10-year IO loan at 6.25%. His IO payment is $5,859/month. The property rents for $7,500/month, giving him positive cash flow of about $1,000/month after taxes, insurance, and management fees. With a fully amortizing 30-year loan, his payment would be $6,930/month, reducing his cash flow to near zero. Michael plans to sell the property in 8 to 10 years for appreciation, so the lack of principal paydown does not concern him. The IO loan maximizes his monthly cash flow during the hold period. He tracks his equity position using our Amortization Calculator to compare against a standard loan.
The Payment Shock Trap
The Chen family buys a $800,000 home with a $640,000 IO loan at 6.25% with a 10-year IO period. Their IO payment is $3,333/month, comfortable on their $180,000 household income. In year 11, the payment jumps to $4,686/month as the $640,000 amortizes over 20 years. Meanwhile, their property taxes increased over the decade, adding another $400/month. Their total housing cost jumps from $4,133 to $5,886, a 43% increase. If their income has not grown proportionally, they may struggle to afford the higher payment. If home values declined and they have no equity, they cannot refinance or sell without bringing cash to closing. This scenario played out for many borrowers during the 2008 financial crisis, which is why IO loans now face stricter qualification requirements.
Why This Calculation Matters
Interest-only mortgages are not qualified mortgages under the Consumer Financial Protection Bureau's Ability-to-Repay rule. This means lenders must manually verify that you can afford the fully amortizing payment, not just the IO payment. The CFPB excludes IO loans from the qualified mortgage category because of the payment shock risk: borrowers who cannot handle the higher payment after the IO period may face default, foreclosure, or forced sale.
The qualification standards for IO loans in 2026 reflect this risk. Most lenders require a 700 to 720+ credit score, 20% down payment (15% on select programs), 43% max DTI calculated at the fully amortizing payment, and 12 to 24 months of PITI reserves. These are stricter than conventional loan requirements. The calculator shows you exactly why: the payment shock can be 30% to 70% or more, depending on the IO period length and the remaining amortization term. Understanding this shock before you sign is the single most important thing you can do with an interest-only mortgage.
Common Mistakes to Avoid
- Not planning for payment shock: The most common and dangerous mistake. Your payment can jump 30% to 70% when the IO period ends. Model the post-IO payment in this calculator and verify you can afford it on your expected income at that time.
- Assuming you will refinance: Many IO borrowers plan to refinance before the IO period ends. But if rates rise, home values fall, or your credit deteriorates, refinancing may not be possible. Have a backup plan that does not depend on refinancing.
- Building no equity during the IO period: During the IO years, your principal balance does not decrease. If home values decline, you could end up underwater (owing more than the home is worth). Consider making voluntary principal payments during the IO period to build a cushion.
- Ignoring the rate adjustment on ARM IO loans: If your IO loan is an ARM, the rate will adjust after the initial fixed period. The adjustment could coincide with or precede the end of the IO period, compounding the payment shock. Stress-test your budget with a rate 2% to 3% higher than the initial rate.
- Qualifying at the IO payment instead of the amortizing payment: Federal law requires lenders to qualify you at the fully amortizing payment, but you should do your own budgeting at that higher number too. Do not let the lower IO payment trick you into borrowing more than you can handle long-term.
Limitations of This Calculator
This calculator models a fixed-rate interest-only loan where the rate stays constant through both the IO and amortizing periods. For ARM IO loans, the rate will adjust after the initial fixed period, which this calculator does not simulate. The actual post-IO payment on an ARM depends on the index value, margin, rate caps, and remaining term at the time of adjustment. The calculator does not account for voluntary principal payments during the IO period, which would reduce the post-IO payment. Property tax and insurance estimates are user inputs and may change over time. This tool does not constitute a loan approval or pre-qualification. Interest-only loans are not available from all lenders and have stricter qualification requirements than standard mortgages. Consult a licensed mortgage professional for an official quote.
Authoritative Research & Resources
- Consumer Financial Protection Bureau: What is an Interest-Only Mortgage? - The CFPB's official guide to interest-only mortgages, explaining how they work, the payment shock risk, and why they are excluded from the qualified mortgage category. Required reading before considering an IO loan.
- Federal Reserve: Guidance on Interest-Only Mortgages - The Fed's supervisory guidance on IO lending standards, including the requirement that lenders assess a borrower's ability to repay at the fully amortizing payment. Provides historical context on why IO loans face stricter underwriting today.
- Freddie Mac Primary Mortgage Market Survey - Current mortgage rate benchmark. As of September 3, 2026, the 30-year fixed averaged 6.71%. IO loan rates typically run 0.25% to 0.50% above comparable fully amortizing rates, so use the PMMS rate as a baseline and add a premium.
- JVM Lending: Interest-Only Mortgage Guide - A practical lender's guide to current IO loan requirements, including credit score minimums (660+ for non-QM, 700+ for jumbo), down payment requirements (10% to 20%), and reserve expectations. Useful for understanding what lenders actually require in 2026.