The Amortization Equal Principal Payments Calculator builds a loan schedule where every period repays the same slice of principal, so the total payment falls each period as the interest charge shrinks along with the balance. Enter a loan amount, an annual interest rate and a term in years, and the calculator lists payment, principal, interest and remaining balance for every period until the loan reaches zero.
This differs from the more familiar fixed-payment loan, where the installment never changes but the interest and principal mix shifts underneath it. Equal principal amortization fixes the opposite piece: the principal portion is locked, and the payment itself moves. Both methods repay the same loan over the same term at the same rate, but they distribute the cash flow differently, and that difference matters for anyone comparing loan offers or building a repayment budget.
*These results are estimates for information only, not lending or financial advice.*
Understand equal principal amortization
Equal principal amortization divides the loan balance evenly across the number of payments, so the principal repaid each period is identical from the first payment to the last.
Interest is then calculated separately on whatever balance remains, which means interest is largest in period one, when the balance is largest, and smallest in the final period, when almost nothing is left to owe.
The principal slice is simple to find: divide the loan amount by the number of periods. A $20,000 loan over 5 years (60 monthly periods) repays a fixed $333.33 of principal every month, no matter what happens to the rate or the balance elsewhere. The Amortization Equal Principal Payments Calculator computes that fixed slice once and then layers the declining interest charge on top of it for each period.
Because the principal piece never changes but the interest piece keeps falling, the total payment declines steadily over the life of the loan. That is the defining signature of this method, and it is the main reason people choose it over a level payment when the loan allows it.
Work through the formula and a full example
The interest charge for any period equals the remaining balance at the start of that period multiplied by the periodic interest rate. The payment for the period is simply that interest charge added to the fixed principal slice: Payment = Fixed Principal + (Remaining Balance x Periodic Rate).
Take the $20,000 loan at 6% annual interest over 5 years again. The periodic (monthly) rate is 6% divided by 12, or 0.5%. In month one, the full $20,000 balance is still outstanding, so interest is 20,000 x 0.005 = $100.00. Added to the fixed $333.33 principal slice, the first payment comes to $433.33. By the time the loan nears its final month, the remaining balance has shrunk to just the last principal slice, so interest is almost nothing and the final payment settles near $335.20 once rounding closes the balance to exactly zero. Across the full 60 months, this loan accumulates about $3,050.00 in total interest.
The Amortization Equal Principal Payments Calculator produces that entire table automatically, so the falling payment path is visible from the first row to the last rather than something you have to compute by hand for each month.
Compare the payment path against a fixed-payment loan
The same $20,000 loan at 6% for 5 years, if repaid with a level fixed payment instead, would carry a constant installment of about $386.66 every month, with total interest of roughly $3,199.35 over the same term.
Notice that the equal principal loan's very first payment, $433.33, is higher than the fixed-payment loan's constant $386.66, but its last payment, $335.20, is lower.
The equal principal method front-loads the cash outflow.
The trade-off is total interest. Because the equal principal loan pays down its balance a little faster on average across the term (the principal slice is fixed and substantial from day one rather than starting small and growing), it typically accrues slightly less total interest than the equivalent fixed-payment loan on the identical principal, rate and term. In this example the difference is about $149.35 over five years, a modest but real saving in exchange for a payment that starts higher and steps down over time.
Borrowers who can absorb a larger payment early, and who value paying less interest overall, often prefer equal principal terms when a lender offers them. Borrowers who need a predictable, unchanging monthly budget figure usually prefer the fixed-payment structure instead.
Read the schedule and plan around a falling payment
Because the payment itself changes every period under this method, budgeting requires looking at more than a single number. The Amortization Equal Principal Payments Calculator's schedule shows exactly how much the payment falls from month to month so the trajectory is clear well in advance rather than a surprise on a statement.
Early in the schedule, the drop from one month's payment to the next is largest, since interest is being charged on the biggest remaining balances and even small balance reductions still leave large interest charges relative to later months. As the loan matures, the payment changes get smaller and smaller until the final payment is barely more than the fixed principal slice itself, because there is almost no balance left to charge interest on.
This declining shape is common in commercial lending, agricultural loans and some student loan structures, where equal principal repayment is either standard or offered as an option. It also appears in some international mortgage markets more often than in typical United States consumer mortgages, which usually default to fixed-payment amortization.
Frequently asked questions
What is equal principal amortization?
Equal principal amortization repays the same fixed slice of loan principal every period while letting the interest charge, and therefore the total payment, decline over time. The Amortization Equal Principal Payments Calculator applies this method directly from loan amount, rate and term.
How is the fixed principal payment calculated?
The fixed principal payment is calculated by dividing the loan amount by the total number of periods. A $20,000 loan over 60 monthly periods repays $333.33 of principal every month regardless of the interest rate applied on top of it.
Why does the total payment fall over time under this method?
The total payment falls because interest is charged on the remaining balance, and that balance shrinks by the same fixed amount every period. As the balance gets smaller, the interest portion added to the fixed principal slice gets smaller too, so the sum of the two declines.
Does equal principal amortization cost less than a fixed payment loan?
On the same principal, rate and term, equal principal amortization usually produces slightly less total interest than a fixed-payment loan, because it repays principal a bit faster on average. On a $20,000, 6%, 5-year loan the difference is about $149 in this example, a real but modest saving.
Is the first payment always higher under equal principal amortization?
Yes, on a loan that would otherwise use fixed-payment amortization, the equal principal method's first payment is typically higher because the full interest charge on the untouched balance is added to a full principal slice right away, rather than being blended into a smaller, level installment.
Summary
The Amortization Equal Principal Payments Calculator repays a loan by holding the principal portion of every payment fixed and letting the interest, and so the total payment, fall as the balance declines.
On a $20,000 loan at 6% over 5 years, the fixed principal slice is $333.33 per month, the first payment is $433.33, the last payment is about $335.20, and total interest over the term is roughly $3,050.00, slightly less than the $3,199.35 a level fixed payment would accrue on the same terms.
The trade-off is a payment that starts high and steps down instead of staying constant. These figures are estimates for planning only, not a lending offer or financial advice.