Why Your First Mortgage Payment Is Almost All Interest

On a $300,000 mortgage at 6%, your very first payment is about $1,500 interest and only $299 principal — not because the bank is gouging you, but because interest is charged on the balance you still owe, and in month one you still owe almost the whole loan. As the balance falls, the split flips: the last payment is nearly all principal. See the full month-by-month breakdown for your own numbers in the mortgage calculator; here’s why it works this way.

The whole idea, in one picture

The one rule that explains everything

Every month, the lender charges interest on the balance you still owe — not on the original loan, and not on what you’ve paid off. The monthly interest rate is the APR divided by 12:

Interest this month = current balance × (APR ÷ 12)

At 6% APR that monthly rate is 0.5%. In month one you still owe the full $300,000, so:

• Interest = $300,000 × 0.5% = $1,500
• Your fixed payment is $1,798.65
• Principal = $1,798.65 − $1,500 = $298.65

So $1,500 of your first payment vanishes as interest and just under $300 chips away at the debt. It feels lopsided because it is — but it’s arithmetic, not a trick. You owe a lot, so you’re charged a lot of interest on it.

Where the fixed payment comes from

The payment is set once, at the start, so that exactly n equal payments zero out the loan. That’s the amortizing-loan formula:

M = P · r(1 + r)ⁿ ⁄ ((1 + r)ⁿ − 1)

where P is the loan ($300,000), r is the monthly rate (0.005), and n is the number of months (360). Plug those in and M ≈ $1,798.65. The mortgage calculator computes this and then walks the schedule forward month by month.

Watching the split flip

Because principal reduces the balance, next month’s interest is charged on a slightly smaller number, so slightly less of the payment is interest and slightly more is principal. That feedback compounds:

Payment	Interest	Principal	Balance after
1	$1,500.00	$298.65	$299,701.35
2	$1,498.51	$300.14	$299,401.20
180 (halfway in time)	≈ $860	≈ $939	≈ $172,000
360 (final)	≈ $9	≈ $1,790	$0

Notice the balance is still around $172,000 at the halfway point in time — you’re not halfway paid off until much later, because those early years barely touched the principal. This is the single most surprising thing about a mortgage, and the reason the equity in a newly-bought home grows so slowly at first.

Why total interest can beat the loan itself

Add up all 360 interest columns and you get roughly $347,500 — more than the $300,000 you borrowed. Total paid: about $647,500 for a $300,000 loan. That’s not unusual; it’s what happens when you borrow a large sum for 30 years. Two levers cut it hard:

• A shorter term. A 15-year loan borrows the money for half as long (usually at a lower rate too), slashing total interest — at the cost of a higher monthly payment.
• A lower rate. Even a fraction of a percent moves the total by tens of thousands over 30 years.

Compare them yourself by changing the term and rate in the calculator and watching the total interest line — the same tool applies to a car loan too, via the auto loan calculator.

The payoff move: extra principal, early

Here’s the lever most people miss. Because interest is charged on the balance, every extra dollar of principal you pay permanently deletes all the future interest that dollar would ever have generated. An extra $200 a month on our example loan doesn’t just pay off $200 faster — it removes years of compounding interest on that money, cutting the term by several years and saving tens of thousands.

And it’s most powerful early, when the balance (and therefore the interest being charged) is largest. The mortgage calculator has an extra-per-month field that shows the exact new payoff date and how many months you’d save — and you can export the full schedule to CSV to plan against it. Everything runs in your browser; none of your figures leave your device.

Quick summary

Mortgage interest is charged on the balance you still owe, so when the balance is highest — at the start — the interest portion of your fixed payment is highest too. On a $300k / 6% / 30-year loan that means $1,500 interest and $299 principal in month one, an even split near the middle, and almost pure principal at the end. The slow early paydown is why total interest (~$347,500) can exceed the loan, and why extra principal paid early is the most effective way to shrink both the term and the total. See your own numbers, schedule and payoff savings in the mortgage calculator.

Sources: standard amortizing-loan mathematics · Consumer Financial Protection Bureau — mortgage basics · Investopedia — Amortization. General educational information, not financial advice.