Monthly private mortgage insurance payment

A premium is a product, not a price

Private mortgage insurance is cover the lender requires and the borrower funds. It does not protect the household, it does not build equity, and it is customary where the loan is large relative to the value of the property — the arrangement under which a lender is carrying more risk than its usual appetite. Understanding whose interest it serves is the first step to reading the figure correctly: it is a cost of borrowing this much against this deposit, and nothing else.

The billing convention is what this calculation encodes. An annual rate is applied to the loan amount to give a yearly charge, and that yearly charge is divided evenly across the months to give the instalment. It is not accrued daily and not recomputed each month against a shrinking balance, which is why the line on a statement usually stays flat while everything around it moves. If a servicer does re-rate against the balance as it falls, the current balance is what belongs in the box — the calculation prices whatever amount it is given.

The premium rate has no default in this pack at all: it is a required input the calculation will not proceed without. That is a deliberate refusal rather than an omission. Premium pricing depends on the size of the deposit, the borrower’s credit profile, the loan programme and the insurer’s own schedule, so there is no single rate that could be carried here without inventing a fact. Take the rate from the offer, the estimate or the statement in front of you.

Because the charge is a product of two numbers, the two trade off against each other in ways that surprise people who think of it as a fixed cost of a small deposit. A modest loan carrying a steep premium rate can cost as much each month as a far larger loan on a gentle one. Borrowing less is only half of the lever; the price attached to the borrowing is the other half, and it is the half that is negotiable between programmes.

What the arithmetic cannot tell you is how long the charge lasts, which is usually the more consequential question. The premium is temporary by design — it ends when the balance has fallen far enough relative to the property — and that timing depends on the schedule rather than on the premium rate. It is computed separately, and the two pages are properly read together: this one for the monthly bite, the other for how many months of it there are.

When this calculation is used

• Adding the premium line to a housing-payment estimate that would otherwise understate what is owed each month.
• Comparing quotes whose premium rates differ because the deposit, the programme or the credit profile differs.
• Putting a monthly figure on a larger deposit, by re-running the same premium rate against a smaller loan.
• Checking an insurance line on a statement or an estimate against the loan amount and rate it claims to rest on.
• Setting up the follow-on question — how many months this line will be paid before it stops.

Worked example

The pack declares three vectors that deliberately move the loan size and the premium rate in opposite directions: a mid-sized loan at a middling rate, the largest loan of the three at the gentlest rate, and the smallest loan at the steepest.

All three land in a strikingly narrow monthly band, even though the largest loan is more than twice the smallest. The largest loan is the dearest of the three per month, but only by a hair; the smallest is the cheapest, again by a hair; and the mid-sized loan at the middling rate falls between them. The rate has very nearly cancelled the size. That is the whole lesson of a premium that is a product: a reader who assumes a big loan means a big premium line, or that a small one means a negligible one, will be wrong in both directions as soon as the rates differ. Both readings are shown, the annual charge and the monthly instalment, the second being the first spread evenly across the year.

The pack also declares a refusal: a loan amount of nothing is declined as a bad input, since there is no balance for a premium to be charged against. And because the rate carries no default, an unpriced premium is left unanswered rather than guessed at. Every figure shown comes from the certified engine at mount; this page stores none.

What each input represents

Assumptions and limits

• The premium is charged on the loan amount entered and held flat for the year; a servicer re-rating against a declining balance requires the current balance to be entered again.
• The annual charge is divided evenly across the months of the year — the standard billing convention, not a daily accrual and not a recomputation on the outstanding balance.
• Only the monthly borrower-paid form is modelled. Lender-paid, single-premium and up-front premium structures price the same cover differently and are not computed here.
• The rate comes entirely from the reader; the pack carries no premium table, no insurer’s schedule and no pricing by deposit size or credit profile.
• Nothing here decides whether cover is required at all, or when it ends — how long the charge runs is a separate calculation on the amortisation schedule.
• The premium sits inside the housing payment alongside principal, interest, taxes and insurance; none of those other components appear here.

What the guards protect against

• A loan amount of nothing or less is refused rather than multiplied out — the range excludes its lower bound, and the pack pins that behaviour with a declared refusal vector.
• The loan amount is bounded above as well, so a figure mistyped by an order of magnitude is declined rather than turned into a premium that still looks plausible on a statement.
• The premium rate is bounded to a narrow band spanning observed pricing at both ends, and it is required with no default, so the calculation never proceeds on an assumed premium price.
• A rate of nothing is admitted and returns no premium. The arithmetic does not decide whether cover applies — it prices the rate it is given, including the absence of one.

Provenance

Borrower-paid private mortgage insurance billing convention

The loan amount multiplied by the annual premium rate supplied as an input to give the yearly charge, divided evenly across the months of the year to give the monthly instalment.

Educational reference, not financial advice, and not a statement of any insurer’s or programme’s pricing — the premium rate is a required input with no default precisely so that no rate is asserted here. The signed pack carries its own citation, which displays from the verified leaf once the calculator loads; the page reports the verification state of the release it mounted rather than asserting one.