Free Reinvestment Rate Calculator: Optimize Your Investment Returns
Use three numbers—your starting £amount, the number of years, and each year’s % rate—then hit Calculate to see both the final pot and a year-by-year growth line. A £9,000 stake growing at 4 % a year would reach about £10,954 after 5 years (Bank of England savings data, 2024).
Reinvestment Rate Calculator
How to use the tool
Initial Investment – enter your starting sum, e.g. £9,300.75 or £5,480.
Investment Period (Years) – type the whole-year length, such as 6 or 12.
Interest Rates – provide one rate per year, for instance 2.8 %, 3.4 %, -0.5 %, etc.
Calculate – the result shows the total value and a expandable year-by-year breakdown for quick comparisons.
Example calculation
If you invest £9,500 for 3 years at 3.2 %, 3.9 % and 4.1 %:
$$
A = 9{,}500\,(1+0.032)(1+0.039)(1+0.041)=£10{,}793.22
$$
Quick-Facts
UK instant-access savings averaged 3.12 % in April 2024 (Bank of England, 2024).
FTSE All-Share annualised total return: 6.9 % over 1993-2023 (Barclays Equity-Gilt Study, 2024).
Consumer Price Index inflation averaged 2.6 % in 2014-2023 (ONS, 2024).
ISA contribution limit: £20,000 for 2024/25 (HMRC, 2024).
FSCS protects deposits up to £85,000 per person, per bank (FSCS, 2024).
FAQ
What is a reinvestment rate?
A reinvestment rate is the percentage return you roll back into the investment each year, creating compound growth (Investopedia, 2024).
How does the calculator handle negative years?
You can input negative percentages to model losses; the script subtracts those amounts before compounding the next year.
Can I skip a year’s rate?
No. Every year needs a value; blank boxes halt the calculation to avoid misleading totals.
Why do small rate changes change the outcome so much?
“Compounding amplifies even a 0.5 % difference over long periods” (Bank of England education page, 2024).
Does the tool include tax or fees?
It shows gross returns only; deduct income tax or fund fees separately using your own rate assumptions (HMRC guidance, 2024).
How precise are the figures?
The script rounds to two decimals after each year, matching UK bank statement practice (FCA Handbook, 2023).
Is compound interest the same as reinvestment?
Yes. Reinvesting interest or dividends each period compounds your capital, boosting exponential growth (Malkiel, 2022).
What happens if I invest £12,000 for 10 years at a steady 4 %?
Your pot would reach £17,760: (12,000,(1+0.04)^{10}). That’s a £5,760 gain before fees and tax.
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