Simple Interest Calculator United Kingdom 2026-27
Quick interest calculation without compounding.
Calculate simple interest in the UK with GBP principal, annual rate, days or years, interest earned, final balance, and non-compounding examples.
UK Simple Interest Notes
UK simple-interest examples are useful for fixed repayment agreements, classroom finance, short-term lending, overdue balances, and straightforward savings comparisons.
Because interest is calculated only on the original principal, the result is simpler than Ofgem or compound-interest comparisons used by many savings accounts.
Use this GBP version when the agreement does not compound and you need a clear interest amount for a chosen number of days, months, or years.
For ISA savings, bank accounts, or investment growth, compare this result with a compound-interest or savings-goal calculation.
UK-specific treatment for simple interest: figures are framed in pounds, with British household or business wording and the assumptions commonly seen in PAYE, HMRC, mortgage, pension, and consumer-credit contexts.
Watch for UK markers in the page copy and inputs: HMRC, PAYE, National Insurance, pension contributions, stamp duty land tax, miles, APR, part-exchange, council tax, VAT, and GBP-based totals.
The result should be read as a United Kingdom estimate, so compare it with UK provider quotes, HMRC or GOV.UK guidance, lender affordability rules, devolved-nation differences, or regulated advice where needed.
Simple interest = Principal × Rate × Time. Interest does not compound — it remains flat.
Select the question that matches where you are right now.
Your result shows the projected growth or return based on the rate, contribution, and time period you entered — using standard compound or simple interest formulas.
Use this to set savings targets, compare investment options, or understand the impact of starting earlier. Adjust the rate and timeframe to model optimistic and conservative scenarios.
Not a guaranteed return. Actual investment outcomes depend on market conditions, fees, taxes, and timing that cannot be predicted with certainty.
Uses standard financial formulas with the inputs you provided. All calculations run in your browser — no data is sent to any server.
Savings and investment results are dominated by three factors: the rate of return, the time horizon, and regular contributions. Compounding amplifies all three over time.
Returns on returns accelerate growth over time. The difference between 5% and 7% over 20 years is much larger than the 2% gap suggests — compounding is non-linear.
Adding even small regular amounts dramatically increases the final balance. £100/week invested at 7% for 20 years grows to over £110,000 in contributions and £110,000+ in returns.
Starting 5 years earlier often produces a larger final balance than doubling your contribution rate. Time is the most powerful variable in savings calculations.
To improve your savings outcome, focus on starting earlier, increasing contributions, and minimising fees and tax drag on returns.
Starting with a small amount today and increasing over time beats waiting to start with a larger amount. Time in the market matters more than timing the market.
A 1% annual fee on a £100k balance costs £1,000/year and compounds against you. Compare fee structures across savings and investment products.
Super, offset accounts, and tax-free thresholds reduce the drag of tax on your returns — letting more of the growth compound for you.
Savings decisions connect to investment, tax, and retirement planning. Use these calculators to model the broader picture.
Work backwards from a target amount to see how much you need to save each month.
Savings goal →Model how an initial investment grows with regular contributions over different time periods.
Compound interest →See what your future balance is worth in today's dollars after adjusting for inflation.
Inflation calculator →How simple interest is calculated
Simple interest formula
Simple Interest = Principal × Rate × Time (P × R × T). Interest is calculated only on the original principal — it never compounds. A £10,000 loan at 5% for 3 years: SI = £10,000 × 0.05 × 3 = £1,500.
| Principal | Rate | Years | Simple interest | Total repaid |
|---|---|---|---|---|
| £5,000 | 5% | 2 | £500 | £5,500 |
| £10,000 | 5% | 3 | £1,500 | £11,500 |
| £20,000 | 7% | 5 | £7,000 | £27,000 |
| £50,000 | 4% | 10 | £20,000 | £70,000 |
Simple interest examples — savings and loans
| Amount | Rate | Period | Simple interest | Monthly interest |
|---|---|---|---|---|
| £5,000 | 4.5% | 1 yr | £225 | £18.75 |
| £10,000 | 5% | 3 yrs | £1,500 | £41.67 |
| £25,000 | 6% | 5 yrs | £7,500 | £125.00 |
| £100,000 | 5% | 2 yrs | £10,000 | £416.67 |
Simple vs compound interest — the difference over time
Why compound interest grows faster
With compound interest, each period's interest is added to the principal and then earns interest itself. With simple interest, the same dollar amount is added each period.
| Time period | £10k at 5% simple | £10k at 5% compound (annual) |
|---|---|---|
| 1 year | £10,500 | £10,500 |
| 5 years | £12,500 | £12,763 |
| 10 years | £15,000 | £16,289 |
| 20 years | £20,000 | £26,533 |
| 30 years | £25,000 | £43,219 |
The longer the period, the greater the advantage of compound interest. At 30 years, compound interest produces 73% more wealth than simple interest at the same rate.
Where simple interest is commonly used
Practical applications
Simple interest is used for: short-term personal loans (some pay-day and personal lenders), car loans (some dealer finance), government bonds, term deposits that calculate interest on the initial deposit only, and some bridging loans.
When savings accounts use compound interest
Most UK savings accounts compound monthly or daily — meaning your interest earns interest. Even if the rate appears the same as a simple interest calculation, the compounding effect means you actually earn slightly more. Always check whether a rate is simple or compound (effective annual rate).
Frequently asked Frequently asked questions
What is the simple interest formula?
Simple Interest = Principal × Rate × Time (P × R × T). Where rate is expressed as a decimal (5% = 0.05) and time is in years. Total amount = Principal + Simple Interest.
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal — the interest amount is the same each period. Compound interest adds each period's interest to the principal, so subsequent interest is calculated on a growing balance. Over time, compound interest produces significantly more growth.
Do UK banks use simple or compound interest?
Most UK savings accounts and term deposits use compound interest (calculated daily or monthly). Most personal loans use compound interest charged monthly. Some short-term loan products and bonds use simple interest. Always check the product disclosure statement.
When is simple interest better for the borrower?
Simple interest loans can be cheaper than compound interest loans at the same rate if the loan is repaid early — because interest does not accumulate on unpaid interest. This is most relevant for short-term loans and early repayment scenarios.
Where these figures come from
Savings and interest figures on this page are drawn from The Bank of England (Bank Rate), HMRC (ISA and savings tax rules), the Financial Services Compensation Scheme (deposit protection), and the Financial Conduct Authority (consumer protection).
- Bank Rate (base rate) — Bank of England — The Interest Rate (Bank Rate).
- ISA annual allowance & rules — GOV.UK — Individual Savings Accounts (ISAs).
- Personal Savings Allowance — GOV.UK — Tax on savings interest.
- FSCS deposit protection (£85,000) — FSCS — Financial Services Compensation Scheme.
- Consumer money guidance — MoneyHelper — Savings.
Last checked: April 2026. Rates and thresholds are reviewed against the source of record each November, when annual adjustments for the following tax year are published.