An amortization schedule is one calculation repeated 360 times on a shrinking balance. This guide reads a single row in full, traces the balance from $200,000 to zero, shows exactly how extra payments bend the schedule, and explains why statements sometimes differ from the clean picture.

One row, fully understood

An amortization schedule is a loan’s whole life in rows, one row per month, and the whole document is understood once a single row is understood, because every row is the same calculation applied to a shrinking balance. Take the first row of a $200,000 loan at 6% over 30 years, with a fixed monthly payment of $1,199.10. The month’s interest is the opening balance times the monthly rate: $200,000 times 0.06 divided by 12, which is $1,000.00. The principal is whatever the payment leaves after interest: $1,199.10 minus $1,000.00, which is $199.10. The closing balance is the opening balance minus the principal: $200,000 minus $199.10, which is $199,800.90. The second row repeats the calculation on $199,800.90, charging $999.00 of interest and $200.10 of principal, and the 360th row charges $5.97 of interest and $1,193.14 of principal, closing the balance to zero. Interest falls, principal rises, the payment never changes, and the balance declines slowly at first and then ever faster. That is the entire schedule, 360 times over, and every insight in this guide is a consequence of those four numbers moving as they do.

The calculator on this site builds both schedules, with and without extras, month by month exactly as described, and the payoff date is counted forward from the start date, today by default, settable under Advanced options. The schedule it shows is the clean amortizing picture: a fixed rate, a fixed payment, no fees, no penalties, no rate changes, and extras applied entirely to principal. Real loans add complications, which the final section lists, but the clean picture is the right foundation, because every complication is a deviation from it, and a deviation can only be understood against a baseline that is understood first. All figures in this guide are worked-example figures at the stated rates, not quotations, and no live rate is claimed.

The shape: slow start, fast finish

Read the balance column down a 30-year schedule and the shape is startling the first time it is seen. After one year, 12 payments of $1,199.10, a total of $14,389.20 paid, the balance has fallen by only $2,456.02, to $197,543.98, because the first year charges $11,933.19 of interest, 83% of everything paid. After five years the balance is $186,108.71, with only $13,891.29 of principal repaid. After ten years it is $167,371.45. After twenty years, two thirds of the way through the term, it is $108,007.17, still more than half the original loan. The halfway point of the balance arrives late, around month 252 on this loan, and the final year is almost all principal: the last twelve payments charge $456.93 of interest in total against $13,932.29 of principal. Borrowers who feel their loan is barely moving in the early years are not imagining it, and borrowers who feel it suddenly accelerates near the end are not imagining that either. Both feelings are the same curve, seen from different ends.

The crossover, the month where principal first exceeds interest in a single payment, is a useful landmark, and on this loan it arrives in month 223, when interest falls to $596.63 and principal rises to $602.48, just past the 18-year mark. Before the crossover, most of every payment is the lender’s. After it, most of every payment is the borrower’s equity. The crossover is not a decision point, nothing should be done differently because it has passed, but it is a morale landmark, and it explains why extra payments have their greatest effect before it: extra principal sent before the crossover cancels interest in the long, interest-heavy stretch that follows, while extra principal sent after it cancels interest in a short stretch that is mostly principal anyway. The schedule’s shape is the reason the timing advice in the companion guide holds, and it is worth seeing in the table rather than taking on trust.

Check the month 180 row against the month 120 row and the acceleration is visible in a single comparison: in the five years from month 120 to month 180, the balance falls by $25,273.76, while in the first five years it fell by $13,891.29, nearly double the progress for the same 60 payments at the same amount. In the five years from month 240 to month 300, it falls by $45,983.00. The payment is constant, the progress is not, and that is the definition of amortization. A borrower who has made 15 years of payments has repaid less than a third of the principal, and a borrower who has made 25 years has repaid nearly 70%. The schedule rewards persistence unevenly, which is why the early years feel unrewarding and the late years feel like a sprint, and why judging a loan by its first-year progress is the wrong measure.

What changes when an extra payment is added

Add $200 a month to the same loan and the schedule changes in a specific, watchable way. The payment column rises to $1,399.10, the interest column falls faster because it is charged on a smaller balance, and the balance column pulls away from the no-extra schedule, month by month, until the loan ends at month 252 instead of 360, with a final part-payment of $701.51. At month 60, the balance with the extra is $172,154.71 against $186,108.71 without it, a gap of $13,954.00, which is more than the $12,000 of extras paid by that point, because the extras have also cancelled interest along the way. At month 120, the balance is $134,595.58 against $167,371.45, a gap of $32,775.87 on $24,000 of extras. At month 240, the balance is $15,598.99 against $108,007.17, and the loan is 12 months from done while the no-extra loan has 10 years left. The gap between the two balance columns at any month is the measure of the plan’s progress, and it grows faster than the extras themselves, because every extra dollar cancels interest in every month that follows it.

The final row also changes character with extras, and it is worth understanding rather than being surprised by. The last payment is almost never a full payment: with $200 extra a month, month 252 charges $3.49 of interest and $698.02 of principal, for a final payment of $701.51, and the loan closes. A borrower who continues paying $1,399.10 after the balance reaches zero has overpaid, and the servicer must refund the excess, but the schedule’s job is to show the exact final payment, and the calculator does so. Similarly, an extra payment larger than the remaining balance, the edge case the calculator’s own worked examples include, a $100,000 extra on a $50,000 balance, closes the loan in one month with only that month’s interest charged. The schedule is a record of a balance declining to zero, and the final row is where the arithmetic meets reality.

Reading the totals: interest, principal, and cost

At the foot of every schedule sit three totals, and they answer three different questions. Total paid, $431,676.38 on the no-extra loan, is the cash that leaves the borrower’s hands over the life of the loan, and it is the number to compare with the price of the house, because it is what the house actually cost. Total interest, $231,676.38, is the lender’s share, more than the original loan itself, which is the figure that shocks first-time readers and should, because it is the true price of borrowing $200,000 for 30 years at 6%. Principal repaid, $200,000, is the loan itself, and it is the only total that does not change when extras are added, because extras change how fast the principal is repaid and how much interest accrues along the way, never how much principal exists. The interest saved by an extra-payment plan, $79,800.51 for $200 a month, is the difference between two total-interest figures, and it is the only honest measure of a plan’s value: the months saved are a consequence, the interest saved is the prize.

One more total is often misread, and it is worth correcting directly. The interest in the first year, $11,933.19, is sometimes described as wasted money, or as money thrown away. It is neither. It is the rent on $200,000 for a year at 6%, and rent is the price of using something that is not yet yours. The alternative to paying it is not paying it, it is not having the house, or having a smaller one, or waiting years to save the price in full while prices and rents move. Interest is the cost of time, and the schedule shows that cost month by month, without flattery and without exaggeration. Whether the cost is worth it is a decision about housing, not about arithmetic, and the schedule’s job is to price the decision, not to make it.

Schedule versus statement: why they differ

A borrower who compares the calculator’s schedule with a servicer statement will sometimes find differences, and the differences have a short list of causes, each checkable. Rate changes: the schedule assumes a fixed rate, and an adjustable-rate loan reprices, changing the payment and every row after the change. Fees and escrow: the schedule models principal and interest only, while a statement payment usually includes taxes and insurance held in escrow, plus any fees, so the statement payment is larger and the principal and interest split must be read from the statement’s own breakdown. Extra-payment application: if extras were held as advance payments rather than applied to principal, the schedule diverges from month one, and the statement will show it in the balance column. Payment timing: a payment credited late, or a first period longer or shorter than a full month, shifts the first row’s interest, and the shift echoes through the schedule in small amounts. Start date: the payoff date counts forward from the start date entered, so a start month entered a year out moves every date by a year without changing any amount. None of these differences means the calculator is wrong or the servicer is wrong. They mean the two documents model different things, and the reconciliation is to align the inputs, rate, balance, start date, and extra-payment application, and then compare again.

The annual overpayment cap, modelled under Advanced options on this site, is the most consequential of the real-world deviations, and it deserves a direct statement. Many UK fixed-rate deals cap penalty-free overpayments at 10% of the balance each year, and extras above the allowance are assumed not paid in the capped schedule, so a $3,000 monthly extra with a 10% cap has $265,329.55 of extras held back over the life of the loan on the calculator’s default example, and still saves $175,200.39. The schedule with the cap is a different schedule, shorter in extras and longer in term, and reading the uncapped schedule as a promise on a capped loan is the one error in this guide that costs real money. Enter the cap as it stands in your loan terms, read the capped schedule, and plan from that one.

Term, rate, and balance: three levers, three different effects

The schedule responds differently to each of its three inputs, and knowing which lever does what prevents the commonest planning errors. Shortening the term, at the same balance and rate, raises the payment and cuts total interest sharply, because the balance has fewer months to earn interest: the same $200,000 at 6% over 15 years costs $1,687.71 a month and $103,788.46 of interest, against $1,199.10 and $231,676.38 over 30 years, a saving of $127,887.92 for a payment $488.61 higher. Lowering the rate, at the same balance and term, cuts both the payment and the total interest, and the schedule’s early rows improve immediately, because the first month’s interest is the balance times the new, lower rate. Reducing the balance, by a down payment, a lump sum, or years of payments already made, cuts the payment if the loan is re-amortized, or shortens the term if the payment is held, and it cuts every future interest row in proportion. Extra payments are, in effect, a way of reducing the balance without re-amortizing, which is why they shorten the term rather than lowering the payment, and why a borrower who wants a lower payment rather than a shorter term must ask the servicer to recast, if the loan allows it, rather than simply prepaying.

Refinancing is the schedule rebuilt from scratch, and it should be judged as a new schedule, not as a tweak to the old one. A refinance that lowers the rate but restarts the term at 30 years can lower the monthly payment while raising total interest, because the balance gets a fresh 30 years to earn interest, and the schedule’s slow start begins again. The honest comparison is total interest and months to clear, old schedule against new, with closing costs added to the new schedule’s balance or counted separately, and the calculator on this site can model the new loan once its balance, rate, and term are known. Never compare a refinance by the monthly payment alone. The schedule exists to prevent exactly that error.

Using the schedule, month by month and year by year

Practically, a schedule is used in three ways. First, as a plan: enter the current balance, rate, and years left, add the extra you can sustain, and read the payoff date, which is the plan’s promise, conditional on the rate staying fixed and the extra being sent. Second, as a tracker: once a year, enter the current balance from the statement, compare it with the schedule’s balance for that month, and investigate any gap, which will be a fee, a rate change, an application difference, or a missed extra, each with its own fix. Third, as a decision tool for lump sums: enter a lump sum as a one-off extra in the month it would be sent, and read how many months and how much interest it removes, which is the lump sum’s true value, comparable across competing uses of the same money. A schedule that is only read once, at the start, is a plan that is never checked, and plans that are never checked drift. A schedule read once a year is a loan under management, and the management is what saves the money.

Keep the schedule with the loan documents, in the same place, and keep the annual check on the same date each year. The habit costs five minutes, it catches servicer errors while they are small, it shows the balance gap widening as extras accumulate, which is the visible reward for a plan that is otherwise invisible month to month, and it turns a 30-year commitment from a background worry into a number that is known, tracked, and shrinking. The schedule is not the loan, and reading it does not pay it, but a borrower who knows the schedule knows the loan, and a borrower who knows the loan makes better decisions about it, every time a decision arrives.

Frequently asked questions

Why is most of my early mortgage payment interest?

Because interest is charged on the opening balance, which is largest at the start. On a $200,000 loan at 6%, month 1 charges $1,000.00 of interest and $199.10 of principal, and the first year charges $11,933.19 of interest against $2,456.02 of principal. As the balance falls, the interest slice shrinks and the principal slice grows, while the payment stays fixed. The crossover, where principal first exceeds interest, arrives in month 223 on this loan.

How do I read the balance column of an amortization schedule?

The balance column is what you still owe after each payment, and it falls slowly at first and faster later. On a $200,000 loan at 6% over 30 years, the balance is $197,543.98 after 1 year, $186,108.71 after 5 years, $167,371.45 after 10 years, $108,007.17 after 20 years, and $0.00 after 360 months. Compare it with the schedule after extra payments: $200 extra a month leaves $172,154.71 at month 60 instead of $186,108.71.

What is the final payment on an amortization schedule?

Almost never a full payment. The loan closes when the balance reaches zero, so the last payment is the remaining balance plus that month’s interest. With $200 extra a month on a $200,000 loan at 6%, month 252 charges $3.49 of interest and $698.02 of principal, for a final payment of $701.51. Continuing to pay the full amount after the balance reaches zero overpays, and the excess must be refunded.

Why does my servicer statement differ from the calculator schedule?

Common causes are a rate change on an adjustable loan, taxes and insurance included in the statement payment through escrow, extras applied as advance payments rather than to principal, payment timing differences, and a different start date. Align the inputs, rate, balance, start date, and extra-payment application, and compare again. An overpayment cap, commonly 10% a year on UK fixed-rate deals, also produces a different, capped schedule.

Does shortening the term or lowering the rate save more?

Both save, differently. Shortening the term on $200,000 at 6% from 30 to 15 years raises the payment from $1,199.10 to $1,687.71 and cuts total interest from $231,676.38 to $103,788.46, saving $127,887.92. Lowering the rate cuts both the payment and the total interest, improving every row from the first. Reducing the balance, through extras, shortens the term without changing the payment. Judge any change by total interest and months to clear, never by the monthly payment alone.

How often should I check my amortization schedule?

Once a year, on the same date. Enter the current balance from the statement, compare it with the schedule’s balance for that month, and investigate any gap, which will be a fee, a rate change, an application difference, or a missed extra. The annual check catches servicer errors while they are small and shows the balance gap widening as extra payments accumulate.