An interest-only (IO) mortgage offers the ultimate temptation: massive purchasing power with incredibly low monthly payments. By completely ignoring the principal balance for the first 5 or 10 years, you can afford a significantly larger home. However, this structure creates a delayed financial time bomb known as "payment shock." Our calculator reveals exactly when that bomb goes off, and how much it will cost you.
Unlike a traditional 30-year fixed mortgage where every payment chips away at the loan balance, an IO mortgage is broken into two strict phases:
Let us assume you borrow $600,000 at a 6.5% interest rate on a 10/20 IO mortgage.
During the first 10 years, your payment is exactly $3,250 a month. That feels affordable.
But in Year 11, the loan fully amortizes over the remaining 20 years. Your new required payment instantly spikes to $4,473 a month. That is a sudden, mandatory increase of over $1,200 a month. If your income has not significantly increased over that decade, you will be forced to sell the house or face foreclosure.
For 95% of homebuyers in 2026, an interest-only mortgage is a terrible idea. However, wealthy investors and high-income earners with variable compensation often use IO loans strategically.
Because your monthly payments do not reduce the principal, the only way you build equity during the first 10 years is if the housing market goes up.
If you buy a house for $500,000 with 0% down on an IO loan, and a recession hits causing home values to drop by 15%, your house is now worth $425,000. But you still owe the bank $500,000. You are "underwater." If you lose your job and are forced to move, you will have to bring $75,000 in cash to the closing table just to sell your own house.
Do not get lured in by the low monthly payment. Run your exact home price through our standard Mortgage Calculator to see what a safe, 30-year fixed loan looks like.
Go to Standard Mortgage CalculatorDuring the initial IO period (e.g., the first 10 years), the bank only requires you to pay the exact amount of interest the loan generates that month. Because you are not paying a single dollar extra toward the principal, the core balance of the debt remains completely frozen.
Calculate your payments during the interest-only period and see how much your payment will jump when the loan fully amortizes.
Total Payments
$975,750
Total Interest Paid
$575,750
If you make minimum payments for the first 10 years, you build zero equity from payments. In year 11, your payment will jump by 37.64%% to $2,982. You must be prepared to handle this “payment shock” or refinance/sell before phase 2 begins.