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If you want a flexible general-purpose tool, start with the main Compound Interest Calculator. If your contributions are monthly, use the Monthly variant. If you are investing inside an ISA, the ISA Growth Calculator adds the tax-free context. For retirement, the FIRE calculator and the Retirement Compound Calculator give you the right framing. Every calculator on this site uses the same underlying engine, the variants differ only in defaults and presentation to match the question you are trying to answer.

Yes. Every calculator uses the standard compound interest formula, A = P(1 + r/n)^(nt) for a lump sum, with the annuity adjustment added on top when you include regular contributions. All formulas are deterministic and transparent. However, projected returns are not guaranteed: real-world investing includes fees, tax (outside an ISA/pension), and market volatility that no simple calculator can predict. Use results as an illustration of what is mathematically possible, not a forecast.

No. Every calculator is free and requires no account. Your inputs stay in your browser, we do not store any of the numbers you enter. You can bookmark a result URL to come back to the same scenario later.

Yes. Most calculators include a year-by-year growth chart and a breakdown of contributions versus interest earned. This is helpful for understanding how compound interest accelerates in the later years, the majority of growth typically happens in the final third of any long-term scenario.

The ISA, LISA, Junior ISA and pension calculators assume tax-free growth (since they are used inside a tax wrapper). The general compound interest calculators do not deduct tax by default, because the correct treatment depends on your personal allowance, tax band, and whether you are inside or outside a wrapper. For UK-specific tax-free projections, prefer the ISA or pension calculators.