Amortization Calculator

This amortization calculator builds a full amortization schedule for any fixed-rate loan. Enter the principal, interest rate, and term, and you get a month-by-month amortization table showing the payment, how much goes to interest, how much goes to principal, and the remaining balance. Use it as a loan amortization calculator for auto loans and personal loans, or as a mortgage amortization calculator for home loans up to 30 years. Add an extra monthly payment to see an amortization calculator with extra payments baked in.

1. Enter your loan amount. This is the original principal. For a mortgage, use the home price minus your down payment. For an auto loan, use the financed amount after trade-in and down payment.
2. Enter the annual interest rate. Use the note rate, not the APR. APR includes fees and is useful for comparing offers, but the amortization schedule is driven by the note rate alone.
3. Select the loan term. Most mortgages are 15 or 30 years. Auto loans run 3 to 7 years. Personal loans are usually 2 to 5 years. The slider above covers all three.
4. Add extra payments (optional). Any extra monthly payment applied to principal compounds savings over the life of the loan. Even $100 extra per month trims several years off a 30-year mortgage and saves tens of thousands in interest.
5. Pick a start date. This sets the calendar dates on every row of the amortization schedule so you can line up real calendar months with your payment number.

The output has three parts. The summary panel shows your monthly payment, total interest paid over the life of the loan, total of all payments, and your payoff date. The annual tab of the amortization table groups payments into loan years, which is the right view for tax planning and year-over-year equity tracking. The monthly tab is the traditional amortization schedule: one row per payment, with principal, interest, and running balance. Scan the first few rows to see how front-loaded the interest is, then scroll to the final rows to see principal dominating the payment.

The math behind every amortization schedule is one payment formula plus two per-month splits. If you want to calculate amortization by hand or in a spreadsheet, these are the three equations you need. They are the same formulas a mortgage amortization calculator or loan amortization calculator uses under the hood.

1. Fixed Monthly Payment

M = P × [ r(1 + r)^n ] ÷ [ (1 + r)^n − 1 ]

Where:
  M = monthly payment
  P = loan principal (starting balance)
  r = monthly interest rate (annual rate ÷ 12)
  n = total number of payments (years × 12)

Example: $300,000 at 7% for 30 years
  r = 0.07 ÷ 12 = 0.005833
  n = 30 × 12 = 360
  (1 + r)^n = 8.1165
  M = 300,000 × (0.005833 × 8.1165) ÷ (8.1165 − 1)
  M = 300,000 × 0.04735 ÷ 7.1165
  M = $1,995.91 per month

2. Monthly Interest Portion

Interest(this month) = Current Balance × r

Example, month 1 of the $300,000 loan above:
  Interest = 300,000 × 0.005833 = $1,750.00

3. Monthly Principal Portion

Principal(this month) = M − Interest(this month)
New Balance = Current Balance − Principal(this month)

Example, month 1:
  Principal = 1,995.91 − 1,750.00 = $245.91
  New Balance = 300,000 − 245.91 = $299,754.09

Quick Reference: Front-Loading on a $300,000 Mortgage at 7% for 30 Years

Every amortization chart shows the same pattern: interest dominates the early payments, principal dominates the final payments. This table tracks the split at four points across the 30-year amortization schedule.

The total payment stays at $1,996 the whole time. Only the split changes. After 10 years of payments you have reduced the $300,000 principal by roughly $43,000, a little over 14% of the loan. After 20 years you have paid down about $130,000, around 43% of the loan. The final decade is where most of the equity is actually built.

Understanding how the amortization formula works is step one. Step two is using that knowledge to spend less on interest. The amortization table above visualizes the cost of the loan; the strategies below show how to shrink that cost without refinancing.

Why Early Payments Save So Much Interest

Every extra dollar you pay toward principal in month 1 saves you 30 years of compounding interest at your loan rate. The same dollar in month 300 saves only 5 years. This is why a single $1,000 extra payment in year 1 of a 30-year mortgage saves more than a $1,000 extra payment in year 15. The calculator above lets you model this directly, but here is the shape of the savings on a $300,000 loan at 7%:

The earlier you hit the principal, the longer that reduction avoids interest. This is the mechanical reason "pay extra now" advice always beats "pay extra later" advice, even though the dollar amount is identical.

15-Year vs 30-Year Amortization

Cutting the term in half does not double the monthly payment, but it slashes total interest by more than half. Compare the same $300,000 principal at 6.5%:

You pay $717 more per month on the 15-year, but save $212,219 in interest. The 15-year is not always the right answer (cash flow flexibility, opportunity cost of investing the $717 elsewhere), but if you can comfortably carry the higher payment and your employer is stable, the savings are real money.

Extra Payment Strategies That Work

Three tactics reliably shorten an amortization schedule without much pain:

1. One extra payment per year. On a $300,000 mortgage at 7%, a single extra $1,996 payment each December takes the loan from 360 months to about 300 months and saves roughly $82,000 in interest. Easiest setup: use a year-end bonus or tax refund.
2. Biweekly payments. Pay half your monthly amount every two weeks. 52 weeks divided by 2 is 26 half-payments, equal to 13 full payments per year instead of 12. This is the "one extra payment per year" trick on autopilot. Confirm your servicer applies the half-payments to principal immediately; some hold the funds and release them monthly, which gives you zero benefit.
3. Round-up method. Round every monthly payment up to the next $50 or $100. A $1,996 payment becomes $2,000 or $2,100. The $4 to $104 extra per month does not sting cash flow but chips steadily at principal. On the $300,000 example, rounding to $2,100 saves about $52,000 and takes 3.5 years off the loan.

When Re-Amortization After a Lump Sum Helps

Re-amortization (also called recasting) is when your lender resets the monthly payment based on the new, lower balance while keeping the original interest rate and term. If you drop $50,000 on a $300,000 mortgage at year 5, the balance falls to roughly $230,000. Without recasting, your payment stays the same and you just finish early. With recasting, the lender recalculates the payment for the remaining 25 years on $230,000, lowering your monthly obligation. Recasting makes sense when you want lower required cash flow (retirement, career change) but keeps all the interest savings of the lump sum. Most lenders charge a small fee ($150 to $500) and require a minimum lump sum of $5,000 to $10,000. Government-backed loans (FHA, VA) generally cannot be recast, only refinanced.