Investments & retirement
See how savings and investments grow over time.
Every calculator in this category is about the same underlying thing: what time does to an amount of money. What differs is whether you are looking forward at a savings balance, backwards at a return, or at what inflation did to purchasing power along the way.
Savings growth and interest
Compound interest calculator
See how savings grow when interest earns interest, with optional regular contributions and a year-by-year chart.
Simple interest calculator
Work out the interest earned and the final balance on an amount at a fixed annual rate over a number of years.
Rule of 72 calculator
Estimate how long it takes money to double, triple, or quadruple at a given annual rate using the rule of 72, 114, and 144.
Savings Calculator
Project how much your savings will be worth with an initial deposit, monthly contributions, an annual interest rate, and a time period.
Investment returns
ROI Calculator
Calculate return on investment (ROI) as a percentage, plus net profit or loss, from an initial investment and a final value. Optionally annualize the return over a holding period.
CAGR calculator
Work out the compound annual growth rate, the total growth, and the total gain from a starting value, an ending value, and a number of years.
Investment return calculator
Work out the total and annualized return on an investment from its starting and ending value over a number of years.
Retirement and purchasing power
Retirement calculator
Project your savings at retirement from your age, current savings, monthly contribution, and expected return — with growth shown separately.
Inflation calculator
Work out the future cost and the future purchasing power of an amount of money from a yearly inflation rate and a number of years.
Compounding is the whole point
Simple interest is always calculated on the original amount. Compound interest is calculated on the amount plus the interest already added — which is why the curve bends upward instead of running straight. Over a few years the difference is small. Over twenty or thirty it is often larger than the deposits themselves, and it is the single biggest factor in long-term saving.
Compound interest calculator shows the difference directly, and Simple interest calculator is the comparison. Rule of 72 calculator gives the quick estimate: divide 72 by the rate and you have roughly the number of years to double.
Nominal return is not real return
A 5% annual return sounds the same in any year, but the purchasing power behind it does not. With inflation at 3%, the real return is closer to 2%, and that is the figure that decides what the money can actually buy at the end. Over long horizons an inflation adjustment is not optional — leave it out and you systematically overstate the result.
Inflation calculator converts an amount between years so you can read the total in today's money.
Total return versus annual return
"Up 60%" means nothing until you know over what period. 60% over three years and 60% over twelve are completely different investments. The compound annual growth rate — CAGR — is the number that makes two histories comparable, because it translates any path into a single annual rate.
CAGR calculator gives that annual rate, Investment return calculator shows both total and annualised return, and ROI calculator is the simple version for a single investment with a clear amount in and out.
Saving and retirement
Savings calculator projects a regular monthly contribution to a final balance, and Retirement calculator adds the horizon to retirement on top. Both run on a rate of return you supply — not a market return fetched from anywhere.
What these calculators do not do
They do not predict markets. A fixed annual return is a modelling assumption, not a forecast — real returns swing, and the order of good and bad years matters, especially close to drawdown. They also exclude tax, platform fees, and ongoing charges, and they are not investment advice. Use them to understand the mechanics and the order of magnitude, not to settle a single decision.
FAQ
- What is the difference between simple and compound interest?
- Simple interest is calculated each year on the original amount. Compound interest is calculated on the amount plus previously added interest, so the base grows every year. Over short periods the gap is modest; over decades it is decisive.
- Why does the rule of 72 work?
- It approximates the mathematical doubling time under compounding. It is accurate enough for mental arithmetic in roughly the 6-10% range and drifts at very high or very low rates. If the number is doing more than sanity-checking, calculate it exactly.
- Should I account for inflation in long-term saving?
- Yes, if you want to know what the amount is worth rather than just how big the number gets. A balance thirty years out looks impressive in today's eyes, but its purchasing power is lower. Run it through the inflation calculator to read it in today's money.
- What rate of return should I enter?
- That is your call — the calculators do not fetch one. A practical approach is to run several scenarios, cautious, middling, and optimistic, and see how sensitive the outcome is. If the spread is wide, the horizon or the contribution is what should change, not the expectation.
- Is CAGR the same as the average return?
- No. Averaging annual percentages overstates the outcome when returns vary, because recovering a loss takes a larger percentage gain. CAGR is the compounded annual rate and describes the actual path correctly.
- Is any of this investment advice?
- No. They calculate on the numbers you enter and take no view on your circumstances, risk tolerance, or time horizon. A significant decision belongs with an adviser who knows your finances as a whole.