What could monthly investing grow to?
Compound growth is the reason a boring global index fund can beat a clever-looking one with high fees. Change the numbers. The cheaper platform fee is often the bigger lever than picking a slightly different tracker.
How index funds work: index funds explained. Vanguard vs HL on fees: Vanguard vs Hargreaves Lansdown. The maths behind this page: compound growth.
Common questions
Does this tell me what I will earn?+
No. It is an illustration using the growth rate you type in. Real returns bounce around, can be negative for years, and are not guaranteed.
What ISA allowance does this use?+
The adult ISA allowance is £20,000 per tax year across cash, stocks and shares, and Lifetime ISAs. If monthly contributions would exceed that, the calculator flags it. Junior ISAs have a separate limit for the child.
Why compare 0.15% and 0.35%?+
Those are typical 2026 platform fees for a simple funds ISA: Vanguard-style 0.15% above £32,000, and Hargreaves Lansdown 0.35% on funds after their 2026 cut. Small pots on Vanguard can pay a £4 monthly minimum instead. Always check live prices.