Mortgage Amortization Calculator
Your mortgage payment looks like one number, but it hides two very different ones: the part that pays down your loan, and the part that pays the bank. In the early years, interest eats almost everything you send, and most borrowers have no idea. This amortization calculator builds your complete payment schedule, month by month: principal, interest, and the balance that remains after every single payment. Once you see it, you will never look at your statement the same way again.
Last updated: October 22, 2026
Your result
The formula
Monthly payment (standard amortization): M = P × r(1+r)^n / ((1+r)^n − 1), where P = loan amount, r = annual rate ÷ 12, and n = total paymentsInterest portion of each payment = remaining balance × monthly rate (annual rate ÷ 12 ÷ 100)Principal portion of each payment = monthly payment − interest portionNew balance after each payment = old balance − principal portionTotal interest over the loan = (monthly payment × n) − loan amountTotal of all payments = monthly payment × number of payments (n = years × 12)Crossover month (when principal first exceeds interest) found by walking the schedule row by row
A worked example
Borrow $400,000 at 6.5% for 30 years and the monthly payment is $2,528.27. In month 1, interest takes $2,166.67 of it and only $361.60 goes to principal, leaving a balance of $399,638.40. By month 60 the split is $2,073.41 interest versus $454.86 principal, with $379,943.18 still owed. The crossover, the first month principal beats interest, does not arrive until payment 234, and by the end you will have paid $910,177.20 in total, of which $510,177.20 is pure interest.
More about the Mortgage Amortization Calculator
What mortgage amortization actually is
Amortization is the process of paying off a loan through fixed, equal monthly payments.
Every payment is split into interest (the bank's cut) and principal (the part that shrinks your balance).
The payment stays the same each month, but the split between the two shifts dramatically over time.
How to read the payment schedule
Each row is one payment: the date, the interest portion, the principal portion, and the balance left after it.
Watch the balance column, that is the number that decides how much interest you owe next month.
Scroll to the crossover month to find when you finally start paying more principal than interest.
Why early payments are almost all interest
Interest is charged on the full outstanding balance, which is at its biggest in the early years.
On a $400,000 loan at 6.5%, the first payment sends 86% of your money to interest and only 14% to principal.
As the balance slowly falls, the interest slice shrinks and more of each payment attacks principal.
What extra payments do to the schedule
An extra $200 a month goes 100% to principal, cutting the balance faster than the schedule shows.
That one change can erase years from the loan and tens of thousands in interest.
Even one extra payment a year, 13 instead of 12, can shave roughly 4 years off a 30 year loan.
15 year vs 30 year: the schedule tells the story
A 15 year loan has higher payments but the crossover month arrives far sooner.
On $400,000 at 6.5%, the 15 year schedule costs about $223,000 in interest versus $510,000 over 30 years.
The schedule makes the trade off visible: monthly affordability now versus lifetime interest later.
Mistakes people make with amortization tables
Assuming half the loan is paid off halfway through, at the midpoint you have usually paid far less principal.
Refinancing late in the loan and restarting the schedule, which throws you back into the interest heavy years.
Ignoring that taxes, insurance, and PMI sit outside the amortization table but inside your real bill.
How the calculator builds your schedule, row by row
The calculator does not estimate your schedule, it rebuilds it exactly the way your lender’s servicing system does, one row at a time. It starts with your opening balance, applies the monthly rate (your annual rate divided by twelve), and splits that month’s payment accordingly.
Take month two of the $400,000 loan at 6.5% from the example above. The balance after month one is $399,638.40, so month two’s interest is $399,638.40 multiplied by 0.065 divided by 12, which is $2,164.71. The remaining $363.56 of the $2,528.27 payment reduces the balance to $399,274.83.
Repeat that loop 360 times and the whole schedule appears: the interest column shrinks by a few dollars each month, the principal column grows by the same amount, and the final row is adjusted by a few cents so the balance lands on exactly zero.
A worked example: what an extra $200 a month really does
Keep the same $400,000 loan at 6.5%, but pay $2,728.27 a month instead of $2,528.27, the standard payment plus $200 marked as extra principal. Because every extra dollar bypasses interest entirely and comes straight off the balance, each following month is charged slightly less interest than the row above it.
Run the schedule with that single change and the loan ends after 293 payments, 24 years and 5 months, instead of 360. Total interest falls from about $510,177 to about $398,286, a saving of about $111,900, and the crossover month, when principal first beats interest, also arrives noticeably sooner.
The lesson hides in the timing: the same $200 added in year twenty saves far less, because by then the balance, and therefore the interest charged on it, is much smaller. Extra payments punch hardest in the early, interest heavy years, which is exactly what the month by month schedule lets you see.
Using the schedule to plan a sale, a move or a refinance
Your remaining balance on any future date is simply the balance in that month’s row, which makes the schedule a planning tool rather than just a record. On the example loan, the balance after ten years of on time payments is $339,104.51, the number a sale or refinance would have to clear.
That is why the schedule matters before you sign a refinance offer. A lower rate on a fresh 30 year term can still cost more overall if it pushes you back into the interest heavy early rows, and comparing the two schedules side by side shows the true break even month.
Lenders can supply their own official schedule for your exact loan, and the figures should match this calculator row for row when the rate, term and start date are the same. Small differences usually come from rounding each month’s interest to the nearest cent, not from a different formula.
How to use the Mortgage Amortization Calculator
- Enter your loan amount, annual interest rate, and loan term in years.
- Hit Calculate to generate your complete month by month amortization schedule.
- Scan the principal vs interest columns and find your crossover month.
- Check total interest and experiment with extra payments to see the savings.
Frequently asked questions
What is a mortgage amortization schedule?
It is a table showing every payment on your mortgage, split into interest and principal, with the remaining balance after each one. Early rows are interest heavy; later rows pay down principal fast. Lenders build it with the standard amortization formula, and this calculator builds the same table instantly for your numbers.
Why is my first mortgage payment mostly interest?
Because interest is charged on the full outstanding balance, which is largest at the start. On a $400,000 loan at 6.5%, the first $2,528.27 payment sends $2,166.67 to interest and only $361.60 to principal. As the balance falls, the interest slice shrinks every month.
When will I start paying more principal than interest?
That is the crossover month, and it comes surprisingly late, around payment 234 on a 30 year loan at 6.5%. Shorter terms and lower rates bring it much earlier. The schedule this calculator builds marks the exact month for your loan.
How much total interest will I pay on my mortgage?
Multiply your monthly payment by the number of payments and subtract the loan amount. On $400,000 at 6.5% over 30 years, that is $2,528.27 × 360 − $400,000 = about $510,177 in interest, more than the loan itself. The schedule shows exactly how that total accumulates.
Do extra payments change my amortization schedule?
Yes, every extra dollar goes straight to principal, which lowers the balance that next month's interest is charged on. Even $200 extra a month can cut years off the loan and save tens of thousands. One full extra payment a year typically removes about four years from a 30 year term.
Does the schedule include taxes and insurance?
No. The amortization table covers principal and interest only. Property taxes, homeowner's insurance, and PMI are escrowed on top by most lenders. Your real monthly bill is higher, but the principal vs interest split in the schedule stays exactly the same.
How is the interest for each month of the schedule calculated?
Multiply the balance left after the previous payment by the monthly rate, your annual rate divided by twelve. On a $400,000 loan at 6.5%, month one charges $400,000 × 0.065 ÷ 12 = $2,166.67. Whatever is left of the fixed payment becomes principal, the balance falls, and next month’s interest is charged on that smaller balance.
Do biweekly payments change my amortization schedule?
Yes. Half a payment every two weeks adds up to 26 half payments a year, thirteen full payments instead of twelve. The extra payment goes entirely to principal, so the balance falls faster, total interest drops and the loan ends earlier than the standard table shows. Ask your servicer to credit the extra amount to principal, not to hold it.
What is negative amortization?
Negative amortization happens when a payment is too small to cover that month’s interest: the unpaid interest is added to the balance, so you owe more after paying than before. It appears with certain adjustable and minimum payment loan designs. A standard fixed rate schedule like the one here can never negatively amortize, because the payment always exceeds the interest due.
Can I build a schedule for a term other than 15 or 30 years?
Yes. The amortization formula works for any term, 10, 20, 25 or any other number of years, and for any loan amount and rate. Enter your exact figures and the calculator builds all the monthly rows, the total interest and the crossover month for that specific loan, which is useful for comparing offers that use non standard terms.