Loan Amortization Calculator
Enter your loan amount, rate, and term to see your monthly payment, total interest, and a complete year-by-year amortization schedule — plus how much extra payments can save you.
What an amortization schedule actually shows you
Every fixed-rate installment loan — mortgages, auto loans, personal loans, student loans — is repaid the same structural way: identical payments every month, with each one split between interest and principal. An amortization schedule is simply the table that breaks that split down payment by payment across the entire loan term, showing exactly how much of each dollar you send in goes toward shrinking the balance versus covering the cost of borrowing.
The split isn't constant. Early payments are interest-heavy because interest is calculated on whatever balance remains, and the balance starts at its highest point on day one. As the balance falls, less interest accrues each month, so a growing share of every identical payment goes toward principal instead — a pattern that becomes very visible once you look at the full schedule rather than just the monthly payment figure.
The amortization formula
M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
M is the fixed monthly payment, P is the loan principal, r is the monthly interest rate (your annual rate divided by 12), and n is the total number of monthly payments over the loan term. This formula is what guarantees the payment stays exactly the same every month while still fully retiring both principal and interest by the final payment — the interest-versus-principal split shifts internally, but the total you send in each month never changes.
Monthly interest, recalculated every month
Each month's interest charge equals the current outstanding balance multiplied by the monthly rate. Whatever's left of the payment after that interest amount is applied directly to reducing the principal balance for the next month's calculation.
Why extra payments compound in your favor
An extra payment reduces principal immediately, which lowers the balance every future month's interest is calculated on — meaning one extra payment early in the loan avoids interest charges for every single remaining month, not just the month it was made.
Worked example: $300,000 at 6.5% over 30 years
Plugging these numbers into the formula gives a fixed monthly payment of approximately $1,896.20. Over the full 30-year term, total payments come to roughly $682,632, meaning total interest paid works out to around $382,632 — more than the original loan amount itself, which is a completely normal outcome for a 30-year mortgage at this kind of rate, not a sign of an unusually bad deal.
Now add a modest $150 extra monthly payment on top of that. The loan pays off roughly 6 years and 4 months early, and total interest paid drops by roughly $74,000 — a striking result from a change that's often well within reach of a typical monthly budget, and exactly the kind of comparison this calculator's extra payment field is built to show.
What actually moves your payment and total interest
| Factor | Effect on Monthly Payment | Effect on Total Interest |
|---|---|---|
| Higher loan amount | Increases proportionally | Increases proportionally |
| Higher interest rate | Increases | Increases, often disproportionately over long terms |
| Longer loan term | Decreases | Increases — more months for interest to accrue |
| Shorter loan term | Increases | Decreases — less time for interest to build up |
| Extra monthly payments | No change to the required payment | Decreases — often substantially |
The term-length trade-off is the one people underestimate most: stretching a loan from 15 to 30 years roughly halves the required monthly payment but can more than double total interest paid, since the balance stays higher for twice as long. There's no universally "correct" choice here — it depends entirely on how much monthly payment flexibility matters to your budget versus minimizing the total cost of borrowing.
Related loan and housing calculators
This calculator handles the core amortization math behind any fixed-rate installment loan, but a mortgage specifically comes with extra pieces — property taxes, insurance, and PMI — layered on top of principal and interest. The mortgage calculator builds those additional housing costs into a full estimated monthly payment, using the same amortization logic as the foundation. If you're still deciding whether buying makes sense at all compared to renting, the rent vs buy calculator puts the numbers side by side directly.
And if a large purchase tied to your loan — furniture, appliances, or a vehicle — comes with a stack of markdowns or rebates applied one after another, the triple discount calculator works out the real final price the same way this tool works out a real final loan cost: step by step, rather than eyeballing a rough estimate.
Loan amortization calculator — FAQ
What does "amortization" actually mean for a loan?
Amortization is the process of paying off a loan through a series of fixed, regular payments, where each payment is split between interest and principal. Early in the loan's life, most of each payment goes toward interest because the outstanding balance is still high; as the balance shrinks over time, more of each identical payment goes toward paying down principal instead. The amortization schedule is simply the table that shows this interest-versus-principal split for every single payment across the life of the loan.
How is the monthly payment calculated?
This calculator uses the standard fixed-payment amortization formula: M = P × [r(1+r)^n] / [(1+r)^n − 1], where P is the loan principal, r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments. This formula guarantees the exact same payment every month while still fully paying off both principal and interest by the end of the loan term, which is why the interest and principal portions shift over time even though the total payment doesn't.
Why does so much of my early payments go toward interest?
Interest for any given month is calculated on whatever balance is still outstanding at the start of that month, and early in a loan the balance is at its highest. On a 30-year mortgage, for example, it's common for well over half of each payment in the first several years to go toward interest rather than principal. This is normal amortization behavior, not a sign of an unusually expensive loan — the same math applies to virtually any fixed-rate installment loan, from mortgages to auto loans.
How much can extra payments actually save me?
Extra payments go straight to reducing principal, which lowers the balance that future interest gets calculated on — meaning every extra dollar paid early in the loan avoids interest for every remaining month of the term, not just the current one. Because of this compounding effect, even a relatively small consistent extra payment can shorten a 30-year mortgage by several years and cut total interest paid by tens of thousands of dollars, which is exactly why the extra payment field in this calculator changes the results as dramatically as it does.
What's the difference between the loan term and the amortization period?
For most personal loans, mortgages, and auto loans, the loan term and the amortization period are the same thing — the number of years over which the loan is scheduled to be fully paid off. In some commercial and specific mortgage products, however, the two can differ: a loan might be amortized as if it will take 30 years to pay off, but the actual term requires refinancing or a balloon payment after only 5 or 10 years. This calculator assumes the term and amortization period match, which covers the overwhelming majority of everyday consumer loans.
Does this calculator account for taxes, insurance, or PMI?
No. This tool calculates principal and interest only, which is the core amortization math common to any type of fixed-rate installment loan. For a mortgage specifically, your actual monthly housing payment often also includes property taxes, homeowners insurance, and possibly private mortgage insurance (PMI) bundled into an escrow payment — those additional costs aren't part of the loan's amortization schedule itself and should be added separately when budgeting your full monthly housing cost.
Why do two loans with the same rate and term produce different payments?
The two variables that change everything are the loan amount and, less obviously, exactly how the rate compounds — this calculator assumes standard monthly compounding, which is the near-universal convention for consumer loans in the United States. If you're comparing an offer from a lender against this calculator's output and see a small mismatch, check whether their quoted rate is the same nominal annual rate or whether fees are being rolled into the effective APR, since that can shift the real payment slightly from a bare interest-rate calculation.
Is a shorter loan term always better than a longer one?
A shorter term almost always means less total interest paid over the life of the loan, since there's less time for interest to accumulate — but it also means a meaningfully higher required monthly payment, since the same principal is being repaid over fewer months. Whether that trade-off is worth it depends on your monthly budget flexibility and other financial priorities; a longer term with a lower fixed payment plus voluntary extra payments when affordable can offer a middle ground, since it keeps the required payment lower while still allowing early payoff when there's room in the budget.
This calculator is for educational purposes only. It is not financial advice. Always consult a qualified financial advisor before making financial decisions.
