How is each payment split between principal and interest?
The calculator first finds the fixed monthly payment for your amount, rate and term. For any given month, it multiplies the balance outstanding before that payment by the monthly rate. That is the interest due. Whatever is left of the payment reduces principal.
The next month starts from the lower balance, so interest is a little smaller and principal a little larger. The principal portion grows by a factor of (1 + monthly rate) each month, which is why the shift is slow at first and accelerates toward the end.
Total interest is the sum of every month's interest portion, which works out to the payment times the number of payments minus the amount borrowed.
Interest(k) = B(k−1) × r Principal(k) = M − Interest(k) B(k) = B(k−1) − Principal(k)
- B(k−1)
- balance before payment k (B(0) is the loan amount)
- r
- monthly rate (annual rate ÷ 12)
- M
- fixed monthly payment
- k
- payment number
Example: splitting payment 1 on a $60,000, 15-year loan
Scenario: Consider $60,000 borrowed at an illustrative 6.9% fixed rate over 15 years, perhaps to buy into a small business or finance land, with monthly payments.
- Monthly rate6.9% ÷ 12 = 0.575% (0.00575)
- Monthly payment$60,000 over 180 months at 0.575% = $535.95
- Payment 1 interest$60,000 × 0.00575 = $345.00
- Payment 1 principal$535.95 − $345.00 = $190.95
- Balance after payment 1$60,000 − $190.95 = $59,809.05
- Payment 2 interest$59,809.05 × 0.00575 = $343.90, so principal rises to $192.05
About 64% of the first $535.95 payment is interest; the loan's total interest is $36,471.00.
Your lender may compute interest by actual days between payments, which shifts these figures by a few cents.
When is a payment breakdown useful?
Deciding when to make extra payments
Seeing how much interest each month carries shows why extra principal early does more good than the same amount near the end.
Understanding a slow-moving balance
If a year of payments barely moved your balance, the breakdown shows exactly how much went to interest instead.
Estimating deductible interest
For loans whose interest may be deductible, the interest portion is the relevant figure, and it is front-loaded.
Planning a sale or refinance
The principal portion tells you how fast you are building equity in whatever the loan bought.
What gets misunderstood about payment composition?
Thinking interest is spread evenly
Interest is not total interest divided by the number of months. It is front-loaded because it follows the balance.
Assuming the payment drops as the balance falls
On a fixed-rate amortizing loan the payment stays level. Only the split changes.
Expecting half the term to clear half the balance
On most loans half the term repays well under half the principal. The midpoint of the balance comes later.
Sending extra money without instructions
Some servicers hold extra funds for the next payment. Ask that extra be applied to principal so it reduces future interest.
When does principal overtake interest?
On the $60,000 example, interest is the larger part of the payment until payment 61, when principal finally edges ahead. The balance does not fall below half the original amount until payment 113 of 180.
Because interest is front-loaded, the first five years account for about 51% of the loan's total interest even though they are only a third of the term. That is the arithmetic behind the common advice that early extra payments go furthest.
| Payment | Interest | Principal | Interest / principal share | Balance after |
|---|---|---|---|---|
| Payment 1 | $345.00 | $190.95 | 64% / 36% | $59,809.05 |
| Payment 12 | $332.57 | $203.38 | 62% / 38% | $57,634.73 |
| Payment 36 | $302.57 | $233.38 | 56% / 44% | $52,386.79 |
| Payment 60 | $268.14 | $267.81 | 50% / 50% | $46,364.66 |
| Payment 61 | $266.60 | $269.35 | 50% / 50% | $46,095.31 |
| Payment 120 | $158.17 | $377.78 | 30% / 70% | $27,130.71 |
| Payment 150 | $87.27 | $448.68 | 16% / 84% | $14,728.87 |
| Payment 180 | $3.06 | $532.89 | 1% / 99% | $0.00 |
Terms used on this page
- Amortization
- Amortization is the process of paying off a loan with equal, regular payments that each cover the interest due for the period plus a slice of principal. Early payments are mostly interest; later ones are mostly principal. By the final payment the balance reaches exactly zero, which is how most car, personal and student loans work.
- Amortization Schedule
- An amortization schedule is a table that lists every payment on a loan and splits each one into interest and principal, along with the remaining balance afterward. It shows exactly how the debt shrinks over time, how much interest you pay in total, and what you would still owe at any point.
- Principal
- Principal is the amount of money you borrow, or the amount you deposit, before any interest. On a loan, it is the balance that interest is charged against, and each payment's non-interest portion reduces it. On savings, principal is your own money, the base on which interest is earned.
- Interest Rate
- An interest rate is the price of money, stated as a percentage of the balance per year. Borrowers pay it to lenders, and savers earn it from banks. The rate alone does not include fees or compounding, so it can understate the true yearly cost of a loan or overstate a simple comparison of savings accounts.
- Simple Interest
- Simple interest is calculated only on the original principal, never on interest already earned or charged. The formula is principal × rate × time. Because interest does not build on itself, simple interest grows in a straight line, which makes it easy to predict and generally cheaper for borrowers than compounding.
Loan Payment Breakdown Calculator: common questions
Why is my first loan payment mostly interest?
Because interest is charged on the balance, and the balance is never larger than at the start. The lender takes that month's interest first, so on a long loan the first payment can be more than half interest. As principal is repaid, the interest portion shrinks month by month. On shorter loans the effect is milder, but the first payment still carries the most interest.
How do I calculate the interest part of a loan payment?
Multiply the balance before the payment by the annual rate divided by 12. On a $60,000 balance at 6.9%, that is $60,000 × 0.00575 = $345.00. Subtract that from your payment to find the principal portion. Repeat with the new balance for the next month. Lenders that use actual-day interest may get slightly different figures.
When does more of my payment go to principal than interest?
It depends on the rate and term. Shorter loans and lower rates cross over sooner; long loans at higher rates can take years. On the illustrative 15-year loan at 6.9%, the crossover comes at payment 61. A full amortization schedule shows the exact month for your loan. Extra principal payments bring the crossover forward.
Does an extra payment reduce interest or principal?
An extra payment applied as principal reduces the balance directly, which lowers the interest charged every following month. It does not change the regular payment on most loans; instead the loan ends sooner. Tell your servicer to apply the extra to principal rather than to future payments. Even small, regular extra payments add up over the life of a loan.
Is total interest divided evenly across payments?
No. Interest is front-loaded, so early payments carry far more than late ones. Dividing total interest by the number of payments gives an average that is too low for the early years and too high for the last ones. Use the month-by-month split instead. The schedule or breakdown is the accurate way to see interest for any year.
Why does the principal portion grow every month?
Because each principal payment shrinks the balance, which cuts next month's interest by that principal times the monthly rate. The payment is fixed, so every dollar of interest saved moves to principal. The growth compounds, which is why the final years repay principal quickly. By the final payment, almost the entire amount is principal.
Does the breakdown change if my rate is variable?
Yes. When the rate changes, the interest portion jumps up or down immediately, and the lender usually recalculates the payment. This calculator assumes a fixed rate, so use it for fixed loans or to see one rate scenario at a time on a variable loan. Rerunning at a new rate after each change keeps the picture current.
How much interest do I pay in the first year of a loan?
Add up the first 12 interest portions. On the $60,000, 15-year example, the first 12 payments include $4,066.13 of interest out of $6,431.40 paid. An amortization schedule or a breakdown like this one is the easiest way to get the exact figure for your loan. That first-year figure is also the largest annual interest total of the loan.
What is the difference between an amortization schedule and a payment breakdown?
A payment breakdown shows how one payment splits between interest and principal. An amortization schedule lists that split for every payment along with the remaining balance. The breakdown answers where this month's money goes; the schedule answers where the loan will stand at any future date. Lenders can usually provide a full schedule on request.
Sources
- Regulation Z (Truth in Lending), 12 CFR Part 1026 — Consumer Financial Protection Bureau. Accessed October 17, 2026.
- Topic no. 505, Interest expense — Internal Revenue Service. Accessed October 17, 2026.
- Consumer Credit – G.19 statistical release — Federal Reserve Board. Accessed October 17, 2026.
We cite primary sources: regulators, central-bank data and federal agencies. Worked examples on this page are our own calculations, last checked October 17, 2026. See our methodology.