Use this calculator to figure out what your monthly loan repayments will be for either fixed-rate or interest only loans. You have the ability to schedule future interest rate changes in your calculation, which will help you see how your loan payments will change if rates rise. If rates fall you can of course remortgage again at the lower rate when your fixed introductory period has concluded.

**Basic Loan Structure:**Enter the price of the home, your down payment and how loan your loan amortisation schedule lasts.**Fixed-Rate Details:**Enter your introductory fixed rate, rate change frequency, anticipated rate changes, and interest rate cap.**Interest-Only Details:**Enter your introductory rate, rate change frequency, anticipated rate changes, and interest rate cap.**Printable Report:**Click on the "printable schedule" button at the bottom of the calculator to create a printable amortisation schedule for your loan scenarios.

Here is the formula for calculating regular amortising monthly repayments.

**Mortgage Payment = P x (r / n) x [(1 + r / n)^n(t)] / [(1 + r / n)^n(t) - 1**]

where

- P = principal
- r = mortgage interest rate as a decimal
- n = number of payments per year (12 for monthly)
- t = loan term in years

Here is the calculation for a 3% APR loan over 25 years

£180,000 x (.03 / 12) x [(1 + .03 / 12)^12(25)] / [(1 + .03/12)^12(25) - 1]

£180,000 x 0.0025 x [1.0025^300] / [(1.0025)^300-1]

£180,000 x 0.0025 x 2.11501955766 / (2.11501955766 - 1)

£450 x 2.11501955766 / (1.11501955766 ) = £853.58/mo

A person could do this calculation by hand, or use the calculator on our homepage to do it faster automatically.

Each time a mortgage's rate changes the above calculation begins anew. So, for example, if after a 5-year introductory rate of 3% the loan jumps to 3.6% you would calculate the new payments likeso:

£153,909.86 (balance from the orignal mortgage after 5 years of payments) at 3.6% APR (the new rate) loan over 20 years (25 years less the 5 years already paid)

£153,909.86 x [(.036 / 12) x [(1 + .036 / 12)^12(20)] / [(1 + .036/12)^12(20) - 1]

£153,909.86 x (0.003) x [1.003^240] / (1.003^240 - 1)

£461.73 * 2.05222004333 / (2.05222004333 - 1)

£461.73 * 2.05222004333 / 1.05222004333 = £900.54

The above formula is for an amortising loan. And each time rates reset you would do the calculation above. The subsequent year if rates changed again you'd insert the balance from the end of that year, shift the loan term from 20 years to 19, and insert the new interest rate.

Each calculation is easy, but doing it by hands dozens of times can get tiring.

The maths on interest-only payments is even easier.

**Interest Only Mortgage Payment = P x** **(r / n)**

£180,000 * .03 / 12

£180,000 * 0.0025 = £450/mo

As rates changed on an interest-only loan you could calculate new payments the same way using the above simple formula. If you ever made any extra payments then you would run the calculation again with the new balance, but otherwise the balance on interest-only loans doesn't change as one is just paying the interest as it accrues.

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