Fixed Rate Mortgage Calculator
Compare the same fixed-rate loan across 15, 20 and 30-year terms to see exactly what a longer term costs in interest and what a shorter one costs in monthly cash flow.
Fixed Rate Mortgage Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Results are a model, not a quotation — an institution's own figures govern.
- Every input is an assumption; change one and the answer changes with it.
- Rounding is applied only at the display layer, so totals may differ by a cent from a statement that rounds each line.
In short: A fixed rate never changes, so the only real decision is term. On $336,000 at 6.5%, thirty years costs $2,123.75 monthly and $428,549.48 in interest, while fifteen years costs $2,926.92 and just $190,845.73 — saving $237,703.75 for $803.17 more per month.
Formula
Only n changes between terms. Because interest accrues on the outstanding balance, halving the term cuts total interest by far more than half.
Worked Example
- Thirty years. $336,000 at 6.5% over 360 months = $2,123.75, interest $428,549.48.
- Twenty years. $2,505.13 monthly, interest $265,230.18.
- Fifteen years. $2,926.92 monthly, interest $190,845.73.
- Compare. Fifteen years costs $803.17 more per month.
- Value the trade. That buys a $237,703.75 interest saving.
Analyst note. The fifteen-year term costs 37.8% more each month but eliminates 55.5% of the interest. In practice the gap is wider still, because fifteen-year loans are typically priced a quarter to a half point below thirty-year loans. The counter-argument is liquidity: a thirty-year loan with voluntary overpayments achieves a similar result while preserving the option to stop.
Strengths & Limits Of This Model
Where this engine is strong
- Runs entirely in your browser — no figure you type is transmitted or stored.
- Shows the full working, so every number can be traced and challenged.
- Free, unmetered and free of affiliate incentives.
Where it stops
- Generalised assumptions cannot capture every individual circumstance.
- Jurisdiction-specific rules and mid-year changes may not be reflected.
- A model output is not a substitute for a professional review of your position.
Practical Use Cases
Choosing a term at application
This is the highest-value decision in the entire mortgage process and is usually made casually. Quantify it here, then check affordability with the Mortgage Affordability Calculator.
Comparing a shorter term against overpaying
A thirty-year loan overpaid to a fifteen-year schedule keeps flexibility that a contractual fifteen-year term removes. Model it with the Extra Payment Mortgage Calculator.
Evaluating a term change at refinance
Refinancing into a fresh thirty-year term resets amortisation and can cost more overall despite a lower rate. The Refinance Calculator settles that.
Methodology & Editorial Standards
All three terms are amortised on the same balance at the same rate so the comparison isolates the effect of term alone. In practice shorter terms carry lower rates, typically a quarter to a half point below thirty-year pricing, which widens the interest saving beyond what is shown here; enter the actual quoted rate for each term for a precise comparison. Total interest is the sum of payments less principal, ignoring escrow, insurance and fees, which do not vary with term. The analysis assumes the loan runs to maturity; borrowers who move or refinance capture only part of the shorter term's benefit. The engine implements the standard published formula for this calculation. Inputs are validated for domain and sign before evaluation, and any undefined case returns an em-dash rather than a spurious value.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Fixed Rate Mortgage Calculator — 20 Expert FAQs
20 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Should I choose a 15 or 30-year mortgage?
Fifteen years saves $237,703.75 of interest but costs $803.17 more monthly. Choose it if the payment is comfortable; choose thirty years and overpay voluntarily if you value the flexibility.
How much interest does a 30-year mortgage cost?
On $336,000 at 6.5%, a striking $428,549.48 — more than the amount borrowed. Total repayment reaches $764,549.48 over the full term.
Why is 15-year interest less than half of 30-year?
Because interest accrues on the outstanding balance, and a fifteen-year schedule reduces that balance far faster. Halving the term cuts interest by 55.5%, not 50%.
Are 15-year rates lower than 30-year?
Typically by a quarter to a half point, since the lender's capital is committed for less time. That makes the real saving larger than this like-for-like comparison shows.
Is a 20-year term a good compromise?
Often overlooked and frequently sensible. At $2,505.13 monthly it costs $381.38 more than thirty years while saving $163,319.30 of interest — most of the benefit at half the budget strain.
What is the advantage of a fixed rate?
Certainty. The payment cannot change for the entire term, which makes long-range planning possible and converts inflation into an advantage as your income rises against a frozen payment.
Can I pay off a fixed-rate mortgage early?
Yes, and prepayment penalties are rare on modern conventional loans. This is what makes a thirty-year loan with voluntary overpayments such a flexible alternative to a shorter term.
Does a longer term mean a bigger house?
It means a bigger loan for the same payment, which is not the same thing. Stretching the term to afford more property is how borrowers end up paying more interest than principal.
What happens to my payment if rates fall?
Nothing — that is the trade-off. You must refinance to capture the lower rate, which involves closing costs and resets the amortisation clock unless you shorten the new term.
Is a 40-year mortgage worth considering?
Rarely. The payment reduction beyond thirty years is small while the interest cost rises steeply, and equity accumulates so slowly that early years build almost nothing.
How does the term affect equity building?
Dramatically. A fifteen-year loan crosses the point where principal exceeds interest almost immediately, whereas a thirty-year loan at this rate does not cross over until month 233.
Should I take a shorter term or invest the difference?
Prepaying returns your mortgage rate guaranteed and tax-free. At 6.5% that is a strong risk-free return, though an employer retirement match beats it and should be captured first.
Is this fixed rate mortgage calculator free to use?
Yes. It is free, requires no account, and has no usage limits. ApexConverter is funded by contextual advertising, never by selling user data.
Is my data sent to a server?
No. The engine runs as Vanilla JavaScript inside your browser under our Zero-Server Client-Side Execution model. Your figures are computed locally and are never transmitted, logged, or stored.
How accurate is this calculator?
It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.
Does it work on mobile?
Yes. The interface is mobile-first with numeric keypad hints and is tested down to a 320-pixel viewport with no horizontal scrolling.
Can I use it offline?
Largely, yes. Because computation is client-side, the page continues to calculate without a network connection once it has loaded.
Which currency does it use?
Amounts display in US$ accounting format, but the underlying mathematics is currency-agnostic. The result is identical in any currency, so simply read the figures in your own.
Why does a result show an em-dash?
An em-dash indicates the calculation is not defined for the inputs given — typically a division by zero or a value outside the valid domain. We show a dash rather than a misleading number.
How do I report an error?
Email apexconverter.praxiscalc@gmail.com with the tool URL, your exact inputs, the output received and the output you expected. Verified mathematical errors are patched within 72 hours.