Mortgage Calculator

Work out the monthly payment on a level-payment or equal-principal mortgage, the total interest, and how much interest and principal you pay each year.

Loan amount

The amount you borrow for the home. Any deposit you put in yourself is not included.

Annual interest rate (%)

The yearly interest rate. The calculator charges one twelfth of it every month.

Term (years)

How long you take to repay, in whole years from 1 to 40. Many mortgages run for 25 or 30 years.

Repayment type

Level paymentsEqual principal

Level payments: the same monthly payment every month. Equal principal: the same part of the loan is repaid every month, so the payment goes down over time.

Monthly payment (first month)

£1,432.25

Level payments

Interest in the first year

£11,904

Total interest

£215,609

Total paid

£515,609

Interest and principal per year

Interest
Principal

Show the table

Year	Interest	Principal
1	£11,904	£5,283
2	£11,689	£5,498
3	£11,465	£5,722
4	£11,231	£5,956
5	£10,989	£6,198
6	£10,736	£6,451
7	£10,473	£6,713
8	£10,200	£6,987
9	£9,915	£7,272
10	£9,619	£7,568
11	£9,311	£7,876
12	£8,990	£8,197
13	£8,656	£8,531
14	£8,308	£8,879
15	£7,947	£9,240
16	£7,570	£9,617
17	£7,178	£10,009
18	£6,771	£10,416
19	£6,346	£10,841
20	£5,904	£11,282
21	£5,445	£11,742
22	£4,966	£12,221
23	£4,469	£12,718
24	£3,950	£13,237
25	£3,411	£13,776
26	£2,850	£14,337
27	£2,266	£14,921
28	£1,658	£15,529
29	£1,025	£16,162
30	£367	£16,820

Remaining balance by year

Remaining balance

Show the table

Year	Remaining balance
0	£300,000
1	£294,717
2	£289,219
3	£283,496
4	£277,541
5	£271,343
6	£264,892
7	£258,178
8	£251,191
9	£243,920
10	£236,352
11	£228,476
12	£220,279
13	£211,747
14	£202,869
15	£193,628
16	£184,012
17	£174,003
18	£163,586
19	£152,746
20	£141,463
21	£129,721
22	£117,500
23	£104,782
24	£91,545
25	£77,770
26	£63,433
27	£48,511
28	£32,982
29	£16,820
30	£0

Total paid, split

Principal £300,000 58.2%
Interest £215,609 41.8%

Total £515,609

Please note: This is an example calculation, not financial advice. Personal circumstances, changes in rules and rates, and additional costs are not included. If in doubt, talk to a financial adviser.

Tax relief on mortgage interest, property taxes, insurance, fees and rate changes during the term are not included.

How this number is calculated

The blocks use your input. Change a value above and they update with it.

Step 1 · Number of months

Term (years)30 × Months per year12 =Number of months360

Step 2 · Monthly interest rate

Annual interest rate (%)4 ÷ Months per year12 =Monthly interest rate0.3333 %

Step 3 · Monthly payment (first month)

(Repayment type: Level payments) (becauseMonthly interest rate0.3333 % does not equal 0 ) Loan amount£300,000.00 × Monthly interest rate0.3333 % ÷ Per100 ÷ 1 − power ofMonthly growth factor1.0033 − Number of months360 =Monthly payment (first month)£1,432.25

Step 4 · Monthly payment (final month)

(Repayment type: Level payments) Monthly payment (first month)£1,432.25 =Monthly payment (final month)£1,432.25

Step 5 · Total interest

(becauseRepayment type1 (Level payments) equals 1 and Monthly interest rate0.3333 % greater than 0 ) Monthly payment (first month)£1,432.25 × Number of months360 − Loan amount£300,000.00 =Total interest£215,609

Step 6 · Total paid

Loan amount£300,000.00 + Total interest£215,609 =Total paid£515,609

How the calculation works

Work out your monthly payment, the total interest and the total amount you pay back. Choose level payments or equal principal and see, year by year, how much of your money goes to interest, how much to principal and how the remaining balance comes down.

A mortgage is repaid in monthly instalments of interest and principal. The interest for a month is the remaining balance times the monthly rate, one twelfth of the annual rate. With level payments (an annuity or repayment mortgage) the payment is the same every month: at the start the balance is high and most of the payment is interest, later more and more goes to principal. With equal principal (a linear mortgage) the same amount is repaid every month, the loan amount divided by the number of months, so the interest and the payment go down a little every month. The calculator uses formulas that give the same result as working through the schedule month by month. Monthly payments are rounded to the cent; totals and yearly amounts to whole units of currency.

Formula

Monthly rate r = annual rate ÷ 12 ÷ 100, number of months n = term × 12. Level payments: payment = loan × r ÷ (1 − (1 + r)^−n), total interest = payment × n − loan. Equal principal: principal per month = loan ÷ n, first payment = loan ÷ n + loan × r, total interest = loan × r × (n + 1) ÷ 2. At 0% interest the payment is loan ÷ n.

Assumptions

The interest rate stays the same for the whole term; each month is charged one twelfth of the annual rate.
Each payment is made at the end of the month, with no extra or missed payments.
Tax relief on mortgage interest and other tax effects are not included: the payment is before tax.
Property taxes, insurance, mortgage insurance, closing costs and other fees are not included.
The loan is fully repaid by the end of the term; interest-only parts and balloon payments are not included.
Monthly payments are rounded to the cent; totals and yearly amounts to whole units of currency.

Example calculations

The button fills in the calculator above, so you can carry on from there.

Level payments over 30 years

Monthly payment (first month)
£1,432.25

Loan amount £300,000.00 · Annual interest rate (%) 4 · Term (years) 30 · Level payments
Level payments over 20 years

Monthly payment (first month)
£1,449.90

Loan amount £250,000.00 · Annual interest rate (%) 3.5 · Term (years) 20 · Level payments
Equal principal over 30 years

Monthly payment (first month)
£2,611.11

Loan amount £400,000.00 · Annual interest rate (%) 4.5 · Term (years) 30 · Equal principal

Frequently asked questions

What is the difference between level payments and equal principal?

With level payments (an annuity or repayment mortgage) the monthly payment is the same every month. With equal principal (a linear mortgage) the same part of the loan is repaid every month, so the payment starts higher and goes down, and the total interest is lower. For 300,000 at 4% over 30 years the total interest is 215,609 with level payments and 180,500 with equal principal.

Why do I repay so little at the start?

Interest is charged on the remaining balance, which is highest at the start. On a level-payment mortgage of 300,000 at 4% over 30 years, 11,904 goes to interest and 5,283 to principal in the first year. In the last year it is 367 interest and 16,820 principal.

Is the monthly payment before or after tax?

Before tax. The calculator shows principal and interest only. Tax relief on mortgage interest, property taxes, insurance and fees are not included, so the amount actually paid each month can be different.

What if the interest rate changes?

The calculator uses one rate for the whole term. In practice a rate is often fixed for a set period and can change after that, and the payment changes with it. Entering a different rate shows the effect on the payment straight away.

Are extra payments included?

No, the calculator follows the regular schedule. An extra payment lowers the remaining balance and with it the interest charged afterwards. How much can be repaid early without a penalty depends on the terms of the loan.

How exact is the result?

The result is the same as working through the schedule month by month, with monthly payments rounded to the cent and totals to whole units. Lenders may round differently or charge interest per day, so their figures can differ slightly.

Sources and checks

How we check it

This calculator has 21 fixed checks: 13 calculations with a result that is fixed in advance, and 8 cases of invalid input that must be rejected. They all run automatically every time we publish; if one fails, the calculator does not go live.

See the calculations

Loan amount £300,000.00 · Annual interest rate (%) 4 · Term (years) 30 · Level payments → Monthly payment (first month) £1,432.25
Loan amount £300,000.00 · Annual interest rate (%) 4 · Term (years) 30 · Equal principal → Monthly payment (first month) £1,833.33
Loan amount £250,000.00 · Annual interest rate (%) 3.5 · Term (years) 20 · Level payments → Monthly payment (first month) £1,449.90
Loan amount £400,000.00 · Annual interest rate (%) 4.5 · Term (years) 30 · Equal principal → Monthly payment (first month) £2,611.11
Loan amount £120,000.00 · Annual interest rate (%) 0 · Term (years) 10 · Level payments → Monthly payment (first month) £1,000.00
Loan amount £120,000.00 · Annual interest rate (%) 0 · Term (years) 10 · Equal principal → Monthly payment (first month) £1,000.00
Loan amount £12,000.00 · Annual interest rate (%) 6 · Term (years) 1 · Level payments → Monthly payment (first month) £1,032.80
Loan amount £2,000,000.00 · Annual interest rate (%) 15 · Term (years) 40 · Level payments → Monthly payment (first month) £25,064.48
Loan amount £2,000,000.00 · Annual interest rate (%) 15 · Term (years) 40 · Equal principal → Monthly payment (first month) £29,166.67
Loan amount £200,619.00 · Annual interest rate (%) 4 · Term (years) 30 · Equal principal → Monthly payment (first month) £1,226.01

Changes

5 October 2026: Clearer help texts for the fields. Sources added and content reviewed.
4 October 2026: First version.

Last reviewed: 5 October 2026 · How we build and check our calculators