Compound interest allows growth to accelerate over time because interest is added to the balance and then earns interest itself. The more frequently interest is compounded, the greater the overall growth.

For example, compounding monthly typically results in a higher final value than compounding annually using the same interest rate and duration.

Because of this, results from a compound interest calculator may differ from simpler investment calculators that assume basic annual growth.

Example 1: The Power of Time (10 Years vs 20 Years)

Imagine you invest a single lump sum of £5,000 into an index fund with an average annual return of 7%, compounding annually:

– After 10 years, your investment will have grown to £9,835 (earning £4,835 in interest).
– If you leave it for 20 years, it doesn’t just double—it grows to £19,348.

Takeaway: In the second decade, you earn almost double the interest you did in the first decade without adding a single extra penny of your own money. That is the power of compounding.

Example 2: Annual vs. Monthly Compounding

Does the compounding frequency really matter? Let’s look at a £10,000 savings account earning 5% over 5 years:

– If interest compounds annually (once a year), you will end up with £12,762.82.
– If interest compounds monthly (12 times a year), you will end up with £12,833.59.

Takeaway: Monthly compounding gives you slightly more money because your interest begins earning its own interest much sooner.