How this works in your browser
The monthly payment comes from the standard amortisation formula, which solves for the fixed payment that will clear the balance exactly over the term given the interest applied each period. The annual rate is divided into a monthly rate and the term converted into a number of payments, so the result is the constant amount a lender would quote for a fixed-rate loan. Total interest is that payment multiplied by the number of payments, less the amount borrowed. It is a mathematical projection rather than a quote: it excludes tax, insurance and fees, and it assumes the rate never changes. Everything is computed in your browser, so your figures are not transmitted anywhere.
Mortgage Calculator vs. typical online calculators
| Feature | Mortgage Calculator (in-browser) | Typical online calculators |
|---|---|---|
| Where the maths runs | In your browser, on your device | Often posted to a server to compute |
| Your inputs are stored | Never - nothing is sent or saved | Frequently logged with your session |
| Works offline once loaded | Yes | No - needs a live connection |
| Ads inside the result area | None | Common on free calculators |
| Account required | No | Often, to save or export results |
| Usage limits | None - free, unlimited use | Sometimes capped per day |
Who uses Mortgage Calculator
Working out affordability
See what a given loan amount costs each month before approaching a lender.
Comparing loan terms
Weigh a lower monthly payment against a much larger total interest cost.
Checking a lender quote
Verify that the payment you were quoted matches the rate and term stated.
Planning a property budget
Work backwards from what you can afford monthly to a realistic price range.
How to use Mortgage Calculator
- 1
Open the Mortgage Calculator
Go to tools.slaytic.com and open the Mortgage Calculator. No sign-up or account required.
- 2
Enter the loan details
Add the amount borrowed, the annual interest rate and the term in years.
- 3
Read the monthly payment
You get principal and interest, plus the total interest over the life of the loan.
- 4
Compare different terms
Run it again at a shorter term to see how much total interest changes.
Frequently asked questions
Does this include property tax and insurance?
No. This calculates principal and interest only. Your actual monthly payment will typically be higher once tax, insurance, and any PMI are included.
Is this a real loan offer?
No. This is a general estimate for planning purposes, not a loan offer or pre-approval. Contact a lender for actual terms.
Can I compare different loan terms?
Yes, run the calculator again with a different term (for example 15 years vs 30 years) to compare the monthly payment and total interest.
Why do I pay so much more interest than principal early on?
Because interest is charged on the balance outstanding, which is at its largest at the start. In the first years of a long mortgage most of each payment goes to interest and very little reduces the debt. That balance shifts gradually, and it is why overpaying early has a disproportionate effect.
What does the total interest figure actually tell me?
It is the number worth looking at hardest, because it is what the loan costs you. A longer term lowers the monthly payment but can add a very large amount to the total, and comparing that figure across terms often reframes what looked like the affordable option.
What is missing from this estimate?
Property tax, buildings insurance, mortgage insurance where required, and any service charges. Together these routinely add a meaningful amount to the monthly figure, so treat the result as the loan portion rather than what will leave your account.
Are the figures I enter sent anywhere?
No. The calculation runs in your browser, so your loan amount and financial position are never transmitted to any lender or comparison service.