Mortgage Interest Split Calculator

Borrowers understand that early payments are mostly interest, and almost nobody knows the actual proportion in a specific year. It is a useful number: in year one of a typical thirty-year loan it is above eighty percent, and by year twenty it has reversed.

This calculator reports the split for whichever year you choose, along with the equity built and the balance at the end of it.

Result

Share going to interest

82.93%

Interest paid that year

$19,093

Principal paid that year: $3,930
Share going to principal: 17.07%
Balance at year end: $316,070
Equity built by payments: $3,930
Monthly payment: $1,919

In year 1, 82.93% of what you pay goes to interest.

The crossover point - where principal first exceeds interest in a single payment - depends on the rate and term, not on the loan size.

Yearly amortization summary

Year	Principal paid	Interest paid	Remaining balance
1	$3,930	$19,093	$316,070
2	$4,172	$18,851	$311,898
3	$4,429	$18,593	$307,469
4	$4,703	$18,320	$302,767
5	$4,993	$18,030	$297,774
6	$5,300	$17,722	$292,473
7	$5,627	$17,395	$286,846
8	$5,975	$17,048	$280,872
9	$6,343	$16,680	$274,529
10	$6,734	$16,289	$267,794

How to use the mortgage interest split calculator

Enter the loan amount, rate and term.
Enter the year of the loan you want to examine.
Read the principal and interest paid in that year and the shares.
Use the yearly table to see how the split moves across the whole loan.

What people use this for

Understanding how little equity the first years actually build.
Estimating interest paid in a year for record-keeping.
Deciding whether a refinance resets you to the expensive part of a schedule.
Explaining amortisation to someone buying a first home.

Worked examples

Every figure below is produced by running this calculator against the example inputs, so the numbers always match the tool.

Year one of a 30-year loan

$320,000 at 6% over 30 years, examining the first year.

Share going to interest: 82.93%
Interest paid that year: $19,093
Principal paid that year: $3,930

Year twenty of the same loan

The same loan two decades in, when the split has reversed.

Share going to interest: 46.78%
Share going to principal: 53.22%
Equity built by payments: $147,189

The reversal takes longer than people expect

On a thirty-year loan at typical rates, principal does not exceed interest in a single payment until somewhere around year eighteen. Before that, most of every payment is rent on the money.

This is why selling or refinancing early in a loan feels like it built almost no equity - because it did not. Equity in the early years comes mainly from the down payment and from price appreciation, not from the payments.

What this means for refinancing

Refinancing into a new thirty-year term restarts the schedule at the point where interest dominates, even at a lower rate. The payment falls and the proportion going to interest jumps back up.

That is not automatically a bad trade - a lower payment has real value - but it is a trade rather than a pure saving, and comparing total interest rather than the payment is the way to see it.

Methodology and assumptions

What this calculator does, and what it deliberately does not do.

The full schedule is built, then the twelve payments of the chosen year are summed for principal and interest.
Equity built is the reduction in balance from the start of the loan to the end of the chosen year. Price appreciation is not included.
A fixed rate is assumed throughout.
Results are estimates. Real quotes depend on credit, income, property, loan programme and lender pricing at the time of application.
Nothing you type is transmitted or stored - the calculation runs entirely inside your browser.

This calculator is provided for informational and educational purposes only. Results are estimates and may not reflect actual rates, fees, taxes, or market conditions.

This website is not a lender, a mortgage broker or a financial adviser. It does not originate loans, does not accept applications and does not forward your details to anyone.

Actual loan terms depend on credit history, income, the property, the loan programme and lender pricing at the time of application. Only a lender can tell you what you qualify for.

Frequently asked questions

Why is so much of my payment interest?

Because interest is charged on the outstanding balance, and early in a loan the balance is at its largest. The proportion falls every month as the balance does.

When does principal exceed interest?

It depends on the rate and term, not on the loan size. On a thirty-year loan at typical rates it is usually somewhere in the late teens.

Does this include equity from price rises?

No. It shows equity built by paying down the balance. Market appreciation is separate and unpredictable.

Can I use this for tax purposes?

It gives the interest paid in a year on the stated assumptions. Your lender’s annual statement is the authoritative figure, and deductibility is a question for a tax professional.

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