Mortgage Principal and Interest Calculator
This mortgage principal and interest calculator computes your exact monthly P&I payment using the standard amortization formula, then shows you a full year-by-year schedule and a chart of exactly how the split between principal and interest shifts over the life of your loan. If you also want property tax, insurance, and PMI folded in, our full Mortgage Calculator covers the complete monthly payment picture.
Skip straight to the calculator ↓Your Loan Details
Your Monthly Principal & Interest Payment
How much of each payment goes to principal vs. interest
Enter your loan details above to see exactly how your payment breaks down.
What If Your Rate Changes?
| Rate scenario | Interest rate | Monthly P&I | Total interest |
|---|
Full Year-by-Year Amortization Schedule
Every year of your loan, showing exactly how much of that year’s payments went to principal versus interest, and your remaining balance.
| Year | Principal paid | Interest paid | Total paid | Remaining balance |
|---|
How to Calculate Mortgage Principal and Interest
Every fixed-rate mortgage payment uses the same amortization formula: M = P × [r(1+r)^n] ÷ [(1+r)^n − 1]. P is your loan amount, r is your monthly interest rate (your annual rate divided by 12), and n is your total number of payments (your term in years times 12). This calculator runs that exact formula, then walks the result forward month by month to build the full schedule below, so every number you see, not just the headline payment, is calculated rather than estimated.
Principal and Interest vs. PITI: What’s the Difference?
Principal and interest, often shortened to P&I, is just the loan payment itself: what you owe the lender for borrowing the money and paying it back over time. It doesn’t include property tax, homeowners insurance, private mortgage insurance, or HOA dues, all of which typically get bundled into your actual monthly mortgage payment through an escrow account. If you want the complete picture of what you’ll actually pay each month on a specific home, our full Mortgage Calculator adds all of that on top of the P&I math shown here.
Why Your Early Payments Are Almost All Interest
This is the single most surprising thing about mortgage math to most first-time buyers: in the first few years of a 30-year loan, the majority of every payment goes to interest, not principal. That’s because interest is calculated each month on your current balance, and early on, your balance is still close to the full loan amount. As you pay down principal, the interest portion shrinks and the principal portion grows, even though your total payment stays the same. The chart above plots this shift directly, and the gauge shows exactly what share of your very first payment is interest.
How Extra Principal Payments Change the Math
Any amount you pay beyond your required monthly payment goes straight to principal, which reduces the balance that next month’s interest is calculated on. Because of how front-loaded interest is, extra payments made early in the loan have an outsized effect on total interest paid and payoff time compared to the same extra amount paid later. Use the extra payment field above to see exactly how many years and how much interest a specific extra amount would save on your loan.
15-Year vs. 30-Year Principal and Interest
A 15-year loan carries a higher monthly P&I payment than a 30-year loan on the same balance, but a meaningfully lower interest rate is common, and total interest paid drops dramatically because you’re both paying down principal faster and paying interest for half as long. A 20-year term sits in between. Toggle the loan term above to compare all four options directly against your own loan amount and rate.
Frequently Asked Questions
What is a mortgage principal and interest calculator?
A tool that computes your exact monthly loan payment using the standard amortization formula, based on your loan amount, interest rate, and term, without including property tax, insurance, or other costs.
How do I calculate mortgage principal and interest by hand?
Use the formula M = P × [r(1+r)^n] ÷ [(1+r)^n − 1], where P is the loan amount, r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments (years times 12).
Why is most of my early mortgage payment interest?
Interest is calculated each month on your current loan balance, which is highest at the start of the loan. As the balance shrinks over time, less of each payment goes to interest and more goes to principal, even though the total payment amount doesn’t change.
What’s the difference between principal and interest and PITI?
Principal and interest (P&I) is just the loan payment itself. PITI adds property tax, homeowners insurance, and often PMI and HOA dues, which is what most homeowners actually pay each month through escrow.
How much do extra principal payments actually save?
It depends on your rate, balance, and how early you start, but because interest is front-loaded, extra payments made earlier in the loan save more total interest and shave more time off the loan than the same extra amount paid later.
Is a 15-year or 30-year mortgage better for principal and interest?
A 15-year loan has a higher monthly P&I payment but typically a lower rate and dramatically less total interest paid, since you’re paying down the balance faster and paying interest for half as long.
Does this calculator include taxes and insurance?
No, this tool isolates the principal and interest portion only. For a complete monthly payment estimate including property tax, insurance, and PMI, use the full Mortgage Calculator linked above.
References
- Consumer Financial Protection Bureau, Owning a Home resources – consumerfinance.gov/owning-a-home
- U.S. Department of Housing and Urban Development, homebuying guidance – hud.gov/topics/buying_a_home
Related DexoCalc Tools
This principal and interest calculator is one piece of a wider mortgage planning toolkit on DexoCalc.
State Mortgage Calculators
Want a full monthly payment estimate for a specific state, including local property tax? These calculators use real local tax data:
This calculator provides estimates for educational purposes only and is not a loan offer, pre-approval, or substitute for advice from a licensed mortgage professional. It calculates principal and interest only; your actual monthly mortgage payment will typically also include property tax, homeowners insurance, and possibly PMI or HOA dues.