Investment Calculator
Model an investment with a starting amount and regular contributions, and see the projected value with inflation-adjusted purchasing power.
How it works
The projection compounds your starting balance and adds each contribution as it arrives. Contributions made early compound for longer, so the timing of money matters nearly as much as the amount.
The inflation-adjusted figure is the one worth reading. A balance that grows 7% a year while prices rise 3% is only gaining about 4% in purchasing power — the nominal number flatters the result, sometimes badly over long periods.
Real markets do not deliver a fixed return each year. A steady rate is a planning tool, not a forecast: the same average with volatile years produces a different outcome, and sequence matters when you are drawing money out.
The formula
Future value
FV = P(1 + r)^t + PMT × (((1 + r)^t − 1) ÷ r)
Real value
real = nominal ÷ (1 + inflation)^t
Real rate
real rate ≈ ((1 + nominal) ÷ (1 + inflation)) − 1
Total contributed
contributed = starting amount + (PMT × periods)
Worked examples
| Scenario | Working | Result |
|---|---|---|
| 5,000 plus 300 a month at 7% for 20 years | Compounded monthly | ≈ 176,000 nominal |
| The same at 3% inflation | Divided by 1.03²⁰ | ≈ 97,000 in today's money |
| Starting 10 years later | Half the time to compound | Far less than half the result |
When you'd use it
- Projecting a retirement or savings pot
- Seeing what an extra 100 a month becomes
- Comparing a lump sum against regular investing
- Understanding what inflation does to a long projection
Common questions
What return rate should I assume?
That is your judgement, not the calculator's. Long-run broad equity averages have been high single digits before inflation, but past averages are not a promise and any single decade can differ sharply. Model a pessimistic case too.
Why is the inflation-adjusted figure so much lower?
Because inflation compounds as well. At 3% a year, prices roughly double in 24 years, so a projection far into the future loses much of its apparent size when expressed in today's money.
Is this financial advice?
No. It is arithmetic on the assumptions you type in. It cannot know your tax position, fees, risk tolerance or time horizon, and it does not model volatility. Use it to explore scenarios, not to decide one.