Finance · housing

Mortgage Calculator

Payment, interest, LTV & PMI, term compare, and a full amortisation schedule.
Fixed-rate amortisation
30-year fixed
Region Multi-region. Costs layered on the payment follow the selected market — US PMI and property tax, UK stamp duty and reverting fixed rates, Canadian CMHC, Australian LMI. The amortisation maths is universal; the costs around it are not.

Set-up

loan basics

LTV 80%

Interest cover ratio, and the rate the rent is tested against. UK lenders use 125% for a basic-rate taxpayer, 145% for higher rate, stressed at the higher of product + 2% and 5.5%.

Taxes, insurance & PMI
Biweekly = 26 half-payments/year (≈ one extra monthly payment).

Loan balance over time

drag along the curve
cumulative principal cumulative interest remaining balance early payments are mostly interest
Important Not financial advice. Every figure here is an illustrative estimate for general information and education. It is not financial, investment, tax, mortgage or legal advice, not a personal recommendation, and not a quote or an offer. Rules of Thumb is not authorised or regulated by the Financial Conduct Authority and does not carry out regulated activities. Rates, fees and thresholds change and may be out of date. Before acting on anything here, speak to a qualified financial adviser, mortgage broker, accountant or your lender, who can take your own circumstances into account. See the Terms of Use.
The step

What happens when the fix ends

payment against the rate you revert to

The revert rate is a guess — nobody knows what they will be offered in five years. A single assumed number gives one confident-looking payment and hides how much it moves. The dashed line is what you pay during the fix; the gap up to the curve is the step.

Monthly costs
Loan detail
Market

How this market works

the model changes, not just the currency
Compare

Same house, three terms

click a card to switch
Schedule

Amortisation table

click a year to expand months
PeriodPaymentPrincipalInterestBalance
Relationships

What drives the payment

markers track your current loan
Field notes

How amortisation actually works

How it works

How to read a mortgage estimate

Start with price, down payment, rate, and term — the four numbers that set principal & interest. Open Taxes, insurance & PMI when you want a fuller monthly picture. Drag the balance curve to inspect any month; compare 15 / 20 / 30-year cards for the interest trade-off; expand the schedule for year-by-year totals.

Worked example

On a $400,000 home with 20% down, you're financing $320,000. At 6.5% over 30 years, the principal & interest payment is about $2,022/mo.

Over the full term that's roughly $408,000 in interest — more than the original loan. Adding just $200/mo extra to principal pays the loan off years early and saves a five-figure sum in interest. At 10% down, LTV is 90% and this tool layers on estimated PMI until the balance falls to 80% LTV.

Why will the rent not support the loan I want?

Because a buy-to-let is underwritten on the rent, not on your salary. The lender divides the annual rent by the interest cover ratio (125% for a basic-rate taxpayer, 145% for higher rate) times a stress rate (usually the higher of your rate plus 2% and 5.5%). That is the largest loan the rent will service, and it is very often smaller than the loan a 25% deposit implies.

Should I take interest-only on a rental?

It is the norm, because the payment is lower and the interest is a cost against rental income. The catch is that nothing is repaid: the full balance falls due at the end and you need a plan for it. Switch the toggle off to see the same loan as a repayment mortgage — the monthly cost rises sharply and the total falls.

Is buy-to-let regulated like a residential mortgage?

Usually not. Most buy-to-let lending sits outside Financial Conduct Authority regulation, so the consumer protections attached to a regulated residential mortgage may not apply. The exception is a “consumer buy-to-let”, broadly where you did not set out to be a landlord — an inherited property, for instance.

Are the typical deposits and rates here real quotes?

No. They are representative market values for orientation, so the page starts you somewhere sensible rather than at zero, and every one is editable. They are not quotes, not sourced from any lender, and they go out of date. Use your own figures, or a broker’s, before deciding anything.

Why is so much of my early payment interest?

Interest is charged on the remaining balance, which is highest at the start. As the balance shrinks, the interest portion of each fixed payment shrinks with it and more goes to principal.

What is PMI and when does it stop?

Private mortgage insurance is typically required when you put down less than 20% (LTV above 80%). Many lenders drop it once LTV reaches 80% through paydown — this tool estimates monthly PMI at your chosen rate and stops charging it once cumulative principal brings LTV to 80% of the original price.

Does a bigger down payment really help that much?

Yes — every dollar down is a dollar you don't finance, plus all the interest it would have accrued. Crossing 20% down often removes PMI entirely, which is a step-change in monthly cost.

What's not included here?

Closing costs (beyond rough awareness), HOA special assessments, rate adjustments (ARMs), refinancing, discount points, and tax deductibility of mortgage interest. Your lender's figure is the one to trust.

Is 30 years always worse than 15?

A 15-year loan pays far less total interest, but the monthly payment is higher. The “right” term depends on cash flow and opportunity cost — use the compare cards above for your numbers.

Results are for reference only. This is not financial advice — verify any numbers you rely on with a lender, advisor, or independent calculator before acting on them.
Version history · 4 releases
  1. v0.582026-07-26Mortgage: six market models (US/UK/CA/AU/EU/NL) that change the maths — compounding, reverting fixes, capitalised insurance, stamp duty, affordability
  2. v0.602026-07-26Fix "undefined" field-note cards on compound-interest and mortgage, and add a build check so card arity cannot break again
  3. v1.152026-07-29Mortgage product types across 6 markets — buy-to-let, FHA/VA, interest-only — with rental stress testing, yield and the stamp duty surcharge
  4. v1.812026-08-09Mortgage: the payment step when a fixed rate ends was computed but whispered — now a headline figure with a sensitivity chart

Releases in which this page changed, newest last. Derived from the archived copy of every release, not from notes written afterwards — so it reflects what actually shipped. Site-wide passes are left out; they are in the full changelog.