How mortgage interest actually works
Mortgage interest runs on one rule: you pay it in arrears, a month behind. That one fact is why your first payment lands six weeks after closing, and why a refinance can “skip a payment” — and why neither is the free gift it looks like. Once you see the timing, the pitches built on it stop working.
I help buyers and refinancing homeowners understand their interest costs in Pittsburgh and across Pennsylvania, Jacksonville and the Beaches, and statewide in Florida and Texas, and I’ve been originating mortgages since 2003.
Your payment pays last month’s interest
Rent works one way: you pay at the start of the month for the month ahead. A mortgage works the opposite way. The interest portion of your payment is charged in arrears — it covers the month that just ended, not the one starting. Your payment due July 1 is clearing the interest that accrued through June. August 1 covers July. And so on, a month behind, for the life of the loan.
That sounds like a technicality. It’s actually the key that unlocks the two things that confuse almost every borrower: the gap before your first payment on a purchase, and the “skipped payment” on a refinance.
Why your first payment is six weeks away — and what you prepaid for it
Close on a home in the middle of June and your first mortgage payment isn’t due July 1. It’s due August 1. Buyers love this — it feels like a free month. Here’s what actually happened.
Because interest is paid in arrears, your first payment can’t be due until a full month of interest has accrued. The first full month you hold the loan is July, and July’s interest comes due — in arrears — on August 1. But what about the back half of June, the days between closing and month-end? You paid that interest at the closing table, as a line item called prepaid, or per-diem, interest.
On a $400,000 loan at 6.5%, interest runs about $71 a day. Close June 12 and you’ll prepay roughly 19 days of June interest — about $1,350 — at closing. Then nothing until August 1, which covers July. You didn’t get a free month; you prepaid June’s tail up front, and your first scheduled payment simply picks up at July.
The lever worth knowing: the later in the month you close, the fewer days of prepaid interest you owe. Close June 25 instead and you prepay about 6 days, not 19 — roughly $925 less cash to close, on the same loan. It won’t change your rate or your long-term cost, but if cash to close is tight, a later closing date is a quiet lever worth using.
The “skip a payment” pitch, and where the money actually goes
The same arrears rule is the engine behind one of the most common refinance pitches: “refinance now and skip a payment — maybe two.” It sounds like found money. It isn’t.
When you refinance, the new loan pays off the old one. That payoff isn’t just your principal balance — it includes the interest that accrued on the old loan since your last payment cleared. You owe that, and it rides along in the payoff, usually financed into the new balance. Then, on the new loan, you prepay per-diem interest from the funding date to month-end, exactly like a purchase. And your new first payment lands a month or so out — so you do go a calendar month, sometimes two, without writing a mortgage check.
But follow the money. The interest didn’t disappear; it got paid in the payoff and prepaid on the new loan. The principal you “skipped” paying down didn’t get paid either — it’s still in your balance, now slightly larger because the bridge interest got financed on top of it. You didn’t skip a payment. You moved it off your calendar and into your loan balance, where it keeps accruing interest for the next 30 years.
The honest read: a skipped payment is a cash-flow convenience, not a saving. It’s the same sleight of hand as a “lower payment” that’s really a longer term — and it’s worth seeing clearly before you let a free-looking month sweeten a refinance that doesn’t otherwise pencil out.
When the numbers do justify a refinance, that’s a good day. But what tells you they do is the break-even math and a clear-eyed look at the APR — not the promise of a skipped payment. The same pattern shows up in the most aggressively pitched refinance of all, the VA streamline, where “skip two payments” is a standard line.
Timing isn’t savings
None of this is a scam — it’s just how amortized interest is structured, and it’s identical on every mortgage at every lender. But timing gets dressed up as savings constantly: a “free” first month, a “skipped” payment, a lower bill that’s really a reset clock. Once you understand that your payment runs a month behind, and that prepaid interest and payoffs quietly square the rest, the pitches lose their magic. You can read a deal for what it actually costs over the time you’ll keep it — which is the only number that matters.
Where this fits
Common questions
Is mortgage interest paid in advance or in arrears?
In arrears, a month behind. Your payment due July 1 clears the interest that accrued through June, and that holds for the life of the loan.
Why is my first mortgage payment not due until six weeks after closing?
Because interest is paid in arrears, your first payment can’t be due until a full month of interest has accrued. Close in mid-June and your first payment is due August 1, which covers July, while the rest of June’s interest was prepaid at closing. It isn’t a free month.
How much prepaid interest will I pay at closing?
It depends on your loan amount, rate and closing date. On a $400,000 loan at 6.5%, interest runs about $71 a day, so closing June 12 means prepaying roughly 19 days of interest, about $1,350.
Does closing at the end of the month save money?
It lowers your cash to close, not your long-term cost. On that same $400,000 loan, closing June 25 instead of June 12 means prepaying about 6 days instead of 19, roughly $925 less at closing, and it won’t change your rate.
Do I really skip a payment when I refinance?
You skip writing a check, not the cost. The interest accrued on your old loan rides along in the payoff, usually financed into the new balance, and you prepay interest on the new loan from the funding date to month-end. A skipped payment is a cash-flow convenience, not a saving.
Just closed, or weighing a refinance?
Send me the numbers and I’ll walk you through exactly what your prepaid interest covered, when your first payment really hits, and — for a refinance — whether a “skipped payment” is hiding a worse deal. No sales calls, no credit pull until you say so.
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