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7–15 yr · What does an extra hundred a month actually buy?

Extra payment

An extra hundred a month does not make next month cheaper. It removes payments from the far end of the schedule, and it takes the interest those payments would have carried with them.

Every figure this page produces is illustrative. The rate you type is an assumption, not an offer; nothing here is a quote, an application or a commitment to lend. The assumptions in force are printed at the bottom of the page.

What you are working from

What you owe now, not what you borrowed.

You type this. It is a number you are testing, not one Plinth is offering.

The years left on the schedule you are on now. A thirty-year loan four years old has twenty-six.

Paid on top of the scheduled payment, from the first month, and applied to principal.

A bonus, a tax refund, the proceeds of something sold. Applied once, to principal.

Counted from now. Earlier is worth more, because it removes interest from every month that follows.

Recalculates as you type. There is no submit button and nothing is sent.

Interest saved Illustrative

$0

—

Payments removed
0

—

Paid off in
—

—

Extra principal you will have put in
$0

—

Your bill next month is $0 either way. Extra principal shortens the schedule; it does not lower the payment. The thing that lowers the payment is arecast — the servicer re-amortises the reduced balance over the remaining term — and not every loan allows one. Ask your servicer whether yours does, what it charges for it, and what minimum lump sum it requires before it will.

Balance owed, with the extra and without it

Two curves from the same starting balance. The gap between them is what the extra principal has removed, and the marked month is where the shorter schedule finishes. The step in the solid curve is the lump sum landing. All figures illustrative.

Balance owed, with the extra and without it

Interest charged, running total, both ways

Both totals climb; the lower one simply stops sooner and flatter. Where the two curves finish, the difference is the interest never charged — which is the saving, and it is not the same thing as money in your hand today.

Interest charged, running total, both ways
Show these numbers as a table

Before you set up the standing order

Tell the servicer it is principal

An extra amount sent without instruction is often held as an unapplied balance or treated as the next month's payment, which does nothing to the balance and nothing to the schedule. Most servicers have a principal-only field or a separate instruction; use it, and check the next statement to see the balance move by the amount you sent.

It is not free money, it is a return

Paying down a mortgage returns exactly the loan rate, guaranteed and untaxed, and it is illiquid — the money is in the house until you sell or borrow against it. Higher-rate debt beats it every time, and so, usually, does an employer match you are not taking. This page deliberately does not compare the two, because that comparison depends on numbers only you have.

The assumptions in force

  • The rate is yours, not ours. Plinth publishes no rates. The figure in the box is an assumption you control, and both curves move with it.
  • Extra principal does not reduce next month's bill. It shortens the schedule. A recast — where the lender re-amortises the remaining balance over the remaining term — is the thing that lowers the payment, and whether your loan allows one is written in your note, not on this page.
  • Every extra dollar is assumed to reach principal in the month you send it. Real servicers vary in how they apply and post extra amounts, and some apply them only at the next scheduled payment.
  • Principal and interest only. Property tax, insurance, HOA dues and mortgage insurance are not modelled here. Conventional PMI in particular is not ended early by extra payments against the original value — automatic termination at 78% is measured against the original schedule, not the one you accelerated.
  • Prepayment penalties are rare on modern owner-occupied mortgages but not extinct. Check your note before you make a large lump sum payment.
  • The payoff dates count forward from this month. They assume the first extra payment goes out next month and none is missed.
  • Nothing here is a quote, an offer, an application or a commitment to lend.

No obligation, and no transmission

Ask a person about this

A broker needs six things to say anything useful. This form asks for exactly those and nothing else — no date of birth, no Social Security number, no credit pull.

This form does not send anything. It validates what you type and then stops. Nothing is stored, nothing is transmitted, no cookie is set and nobody will call you. The demonstration is the point — on a real build one function call inLeadForm.astro would hand this to a CRM.

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