What a demand loan or call loan is
A demand loan has no fixed term. The lender can call it in at any time and the borrower can usually repay at any time, so the question is not a monthly payment but how much interest has built up to a given date. A call loan is the same thing under another name. Simple interest is charged on the balance outstanding, and the interest is not added to the balance.
Worked example: £15,000 with one part-payment and a rate change
£15,000 is lent on 2 March 2026 at 6.5% a year. £2,000 is paid on 1 May, the rate rises to 7.5% on 1 July and the loan is settled on 2 September. Over 184 days, interest charged comes to £473.59. The £2,000 first clears the interest built up to 1 May and the rest reduces the balance, leaving £13,160.27 owed with £313.32 of interest unpaid, so £13,473.59 clears the loan on 2 September.
Published examples reproduced
Gatehouse Chambers' simple interest calculator counts both the first and the last day. For £10,000 at 8% a year from 15 January to 14 May 2026 it gives 120 days and £263.01, and with the option to count both days this calculator gives 120 days and £263.01. A monthly rate is multiplied by 12 first: 0.5% a month on £10,000 from 1 January to 31 March 2026 is 90 days and £147.95.
Days in the year and how days are counted
Interest for a day is the yearly rate divided by the days in the year. Gatehouse uses the real length of the year, so 8% on £10,000 for the whole of 2024 is £800.00 over 366 days. On a fixed 365-day basis the same 366 days costs £802.19. This calculator offers 365 days (the default), 360 days and actual days in each year, and either counting the days between the dates or counting both the first and the last day. Check your loan terms for which applies.
Part-payments, advances and rate changes
A part-payment pays the interest built up so far first and then reduces the balance. If it is smaller than the interest, the unpaid interest carries forward and the balance does not fall: a £50 payment on 1 April against £15,000.00 lent leaves the full balance and £441.51 of interest unpaid at the end. An advance adds to the balance from its date, and a rate change applies from its date. Interest for each stretch is rounded to the penny, as in a repayment schedule.
For a loan with a fixed term, use the simple interest loan calculator.
If you meant a car loan, use the car finance calculator.
What this does not cover
Interest here is simple: unpaid interest is not compounded. Whether a particular loan is regulated credit, the interest a court might award, and statutory interest on late-paid business invoices are different questions with different rules, and are not calculated here. Take advice on a dispute.
Use the right country page
This page uses pounds and UK-style dates. For a US demand loan, in dollars and with US tax notes, choose United States above the form to open the US page. Inputs reset and amounts are not converted.
Inputs for the demand loan calculator
Amount borrowed and interest rate
The balance on the start date and the simple rate. Choose whether the rate is per year, month, week or day.
Days in the year and counting days
365, 360 or actual days; days between the dates, or counting the first and last day as well.
Loan start date and settlement date
Interest runs from the day after the start date up to the settlement date.
Part-payments
How many payments you make before settling, each with a date and an amount.
Further advances
Extra money lent after the start, each with a date and an amount.
Rate changes
Dates when the rate changes, each with the new rate for the same period as the rate above.
CALCULATOR QUESTIONS
UK demand loan calculator questions
How is interest on a demand loan calculated?
Simple interest on the balance outstanding: balance times yearly rate times days, divided by the days in the year, worked out for each stretch between events and rounded to the penny.
Is a call loan the same as a demand loan?
Yes. Both can be called in by the lender at any time, and this calculator covers both.
How much does 8% cost on £10,000 for a year?
For 2024, a leap year counted by actual days, £800.00. On a 365-day basis the 366 days cost £802.19.
What happens if I pay less than the interest owed?
The unpaid interest carries forward and the balance stays the same. It is not added to the balance, so no interest is charged on interest.
Can I use it for a car loan?
No. A car loan has a fixed term and monthly payments. Use the car finance calculator.