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Mortgage Amortization Schedule Calculator

Calculate total interest paid, monthly payment, and every month's principal/interest split for any fixed-rate loan — then see how extra payments cut years off your term.

Inputs

$

The original or current principal balance — not the home price. For a new loan this is your financed amount; for an existing loan use your current payoff balance.

%

Your fixed annual interest rate. Check your note or monthly statement.

Original term of the loan.

$

Additional principal you pay each month on top of the regular payment. Even small amounts reduce total interest and shorten your term.

Results update as you type, and the address bar keeps your numbers so the link you share reopens this exact calculation.

Total interest paid

$446,428

Over 360 months at 7% annual rate

Monthly payment (P&I)

$2,129

Principal and interest only; taxes, insurance, and PMI are excluded.

Detailed results
Total amount paidTotal of all payments including principal repayment.$766,428
Interest-to-principal ratioDollars of interest per dollar of principal borrowed.1.4

What this result means

Total interest paid: $446,428.

A $320,000 loan at 7% for 30 years requires a fixed payment of $2,129/month. Over 360 payments you pay back the original $320,000 in principal plus $446,428 in interest — a total of $766,428. The interest-to-principal ratio of 1.40 means you pay $1.40 in interest for every $1.00 borrowed.

Month-by-Month Amortization Schedule

Every period's payment breakdown: how much goes to interest versus principal, the remaining balance, and running totals. The schedule stops at payoff — earlier than the original term if you are making extra payments.

Month-by-Month Amortization Schedule. 360 rows, first 12 shown.
MonthPaymentExtra PrincipalPrincipalInterestCumulative InterestRemaining Balance
1$2,129$0.00$262$1,867$1,867$319,738
2$2,129$0.00$264$1,865$3,732$319,474
3$2,129$0.00$265$1,864$5,595$319,208
4$2,129$0.00$267$1,862$7,457$318,942
5$2,129$0.00$268$1,860$9,318$318,673
6$2,129$0.00$270$1,859$11,177$318,403
7$2,129$0.00$272$1,857$13,034$318,131
8$2,129$0.00$273$1,856$14,890$317,858
9$2,129$0.00$275$1,854$16,744$317,583
10$2,129$0.00$276$1,853$18,597$317,307
11$2,129$0.00$278$1,851$20,448$317,029
12$2,129$0.00$280$1,849$22,297$316,749

How this is calculated

M = P · r(1+r)^n / ((1+r)^n − 1)
where: P = principal, r = annual_rate / 12, n = term_years × 12

Total interest = Σ (balance × r) for each period until balance = 0
With extra payment: each period's principal payment = M − interest + extra_payment; stop when balance ≤ 0

How mortgage amortization works

When you take out a fixed-rate mortgage, every monthly payment is the same dollar amount from the first month to the last. What changes over time is how that payment is split between interest and principal. In the early years the vast majority of each payment covers interest; by the final years nearly all of it retires principal. This front-loading of interest is not a trick — it is the natural result of the amortization formula.

The formula

The standard monthly payment formula is:

M = P × r(1+r)^n / ((1+r)^n − 1)

where P is the loan principal, r is the monthly interest rate (annual rate ÷ 12), and n is the number of monthly payments (years × 12). Every element is fixed at origination, so M never changes.

Each month the lender applies your payment in two steps. First, multiply the remaining balance by the monthly rate to get interest owed. Second, subtract that interest from M to get the principal reduction. Because the balance is highest at the start, so is the interest charge — leaving very little of each early payment to reduce principal.

Why front-loading matters

On a $320,000 loan at 7% for 30 years the monthly payment is about $2,129. In month one, $1,867 of that goes to interest and only $262 reduces the balance. By month 180 (year 15) the split is closer to $1,400 interest and $729 principal. By month 348 (year 29) it flips entirely: less than $100 goes to interest. The loan pays off in month 360 exactly.

Over the full 30 years you pay back $320,000 in principal plus roughly $446,000 in interest — more than the original loan again. This is not unusual; it is what a 7% rate costs over three decades.

How extra payments change everything

Because each payment is applied first to interest (which is determined by the remaining balance), any extra principal you pay today eliminates interest charges on that balance for every remaining month. A $500 extra principal payment in month one saves interest on that $500 for 359 future months. The same $500 in month 200 saves interest only for the remaining 160 months. This is why starting extra payments early, rather than late, produces disproportionately large savings.

On the same $320,000 / 7% / 30-year loan, adding just $500/month in extra principal cuts total interest paid by roughly $207,000 and shortens the term from 360 months to about 213 months — nearly 12 years early.

Reading the schedule

Each row of the schedule shows one month's breakdown. The "Cumulative Interest" column is the most telling: it grows steeply in the early years and flattens toward the end, tracing the amortization curve. The "Remaining Balance" column shows how slowly the balance falls in the early years versus how quickly it falls at the end. If you have ever made several years of payments and checked your balance only to find it barely moved, you have witnessed amortization front-loading firsthand.

When to use this calculator

This calculator is designed for any fixed-rate installment loan — mortgages, auto loans, personal loans, or home equity loans all amortize the same way. Use it to understand the true cost of borrowing at a given rate and term, to see how extra payments affect your payoff date and total interest, and to decide whether paying down principal faster is a better use of cash than alternative investments.

Assumptions

  • The interest rate is fixed for the entire loan term; adjustable-rate mortgages require a separate model.
  • Payments are made monthly, on time, with no grace-period interest or late fees.
  • Extra payments are applied entirely to principal at the time of the regular payment, not held for the next payment cycle.
  • The amortization schedule uses exact daily math approximated as a monthly rate (annual rate ÷ 12) applied once per period — actual lender calculations may use actual/365 or 30/360 day counts.
  • Reported totals cover principal and interest only; property taxes, homeowners insurance, PMI, and HOA dues are excluded.
  • Rounding: each period's interest and principal are computed in full precision; the final payment absorbs any cent-level remainder.
  • No balloon payment, prepayment penalty, or interest-only period is modelled.
  • The loan is originated fresh at the stated principal — for existing loans, use the current payoff balance, not the original loan amount.

Frequently asked questions

›Why do I pay so much interest at the start of a mortgage?

Each month's interest charge is your remaining balance multiplied by the monthly rate. At the beginning the balance is at its maximum, so the interest charge is at its maximum. Because your total payment is fixed, that high interest charge leaves little room for principal reduction. As the balance slowly shrinks, so does the interest portion, freeing up more of each payment for principal. This self-reinforcing dynamic — called amortization front-loading — is a mathematical property of any fixed-payment installment loan.

›How does an extra monthly payment reduce total interest so dramatically?

Every extra dollar of principal paid today eliminates interest on that dollar for every remaining month of the loan. At 7%, one dollar saved in principal saves roughly $0.0058 in interest the next month, $0.0058 the month after, and so on until payoff. Over hundreds of months, that compounds into substantial savings. The earlier in the loan you make extra payments, the more months benefit — which is why even a modest extra payment started early produces outsized results.

›Does the payment change if I make extra principal payments?

No. Your contractual monthly payment stays the same. Extra payments reduce the principal balance faster, which means the loan pays off earlier, but the lender does not recalculate your required payment. Some borrowers mistake the lower balance for a lower payment obligation — it is not. You still owe the same payment each month; the loan just ends sooner.

›What is the interest-to-principal ratio and what is a good number?

The ratio tells you how many dollars of interest you pay for each dollar you borrow. A 30-year loan at 7% has a ratio near 1.40 — for every $1 borrowed, you pay about $1.40 in interest by payoff. A 15-year loan at 4% might have a ratio around 0.33. There is no universal 'good' number; it depends on the rate and term. A lower ratio means the loan costs less overall, which is why shorter terms and lower rates are preferable when affordable.

›Can I use this calculator for loans other than a mortgage?

Yes. Any fixed-rate installment loan — auto loans, personal loans, student loans, home equity loans — amortizes using the same formula. Enter the original or current balance, the annual interest rate, and the term. The schedule and totals will be accurate regardless of loan type.

›Why does my actual payoff date differ from what the calculator shows?

This calculator assumes payments on the same day each month with no gaps. In practice, payment timing, rounding to the nearest cent, and the way your servicer applies payments can create small differences. Some lenders also apply extra payments to future required payments rather than to principal unless you explicitly designate them — always confirm with your servicer that extra amounts are applied to principal immediately.

›Should I make extra mortgage payments or invest the difference?

This is one of personal finance's most debated questions. Making extra payments is a guaranteed, risk-free return equal to your mortgage interest rate. Investing instead offers potentially higher long-run returns but with volatility and tax implications. If your after-tax investment return exceeds your after-tax mortgage rate, investing tends to win mathematically. If your mortgage rate is above what you expect to earn after tax, paying down the loan wins. Many people choose a middle path for the psychological benefit of debt reduction alongside market participation.

›What is the difference between this calculator and a mortgage payment calculator?

A mortgage payment calculator answers 'what is my monthly payment?' given a home price, down payment, and rate. This amortization calculator assumes you already know your loan amount and focuses on the full picture: total interest paid, the month-by-month breakdown, and how extra payments change your outcome. Use a payment calculator to size a new loan; use this one to understand what that loan costs over its life.

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