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Position Math

Calculators › Investing

Investment Calculator (Monthly Contributions + Compounding)

Project what a regular monthly investment could grow to. Enter an optional starting lump sum, your monthly contribution, an expected annual return and a horizon, and see the future value, total invested, gain and year-by-year growth path.

Your plan

FV = P₀(1+r)ⁿ + Σ PMT(1+r)ᵏ  ·  r = annual return / 12

Projection

Future value—
Total invested—
Total gain—
Growth multiple—
Growth path—
Portfolio valueMoney invested
Enter a monthly amount and an expected return to project your portfolio.

How it works

What this calculator does

It compounds your money month by month. Each month it adds your contribution and grows the balance by one-twelfth of your expected annual return, for the whole horizon. This is the standard dollar-cost-averaging / SIP future-value model.

The formula

For an initial amount P₀, a monthly contribution PMT, a monthly rate r = annual / 12 and n months:

FV = P₀(1+r)ⁿ + PMT · ((1+r)ⁿ − 1) / r

Contributions at the start of the month earn one extra month of growth, so that term is multiplied by (1+r). When the annual step-up is above zero, each year's contribution is raised by that percentage and the months are rolled forward exactly, which is why this tool simulates month by month instead of using a single closed form.

Worked example

$500 a month for 20 years at 8% a year, no lump sum, end-of-month: you invest $120,000 and the projection grows to about $296,000 — roughly 1.5x your gain on top of what you put in, purely from compounding a constant assumed return.

What it deliberately does not do

It assumes a single constant return; real markets are volatile and sequence-of-returns matters. It does not model taxes, fees beyond what you bake into the return, currency, or withdrawals. Use it to compare plans and see the shape of compounding, not as a forecast.

Frequently asked questions

How is the future value of monthly investing calculated?
Each month your contribution is added and the balance grows by one-twelfth of the expected annual return. Over n months that is FV = P₀(1+r)ⁿ + PMT·((1+r)ⁿ−1)/r, where r is the monthly rate. This tool runs that month by month so step-ups and timing are exact.
What return should I assume?
There is no right number — it is your assumption. Broad equity indices have historically returned roughly 7–10% a year before inflation over long periods, but any single decade can be very different. Try a range (e.g. 5%, 8%, 10%) to see how sensitive the outcome is.
What does the annual step-up do?
It raises your monthly contribution by a fixed percentage every year, modelling the common habit of investing more as income grows. A 10% step-up means year two invests 10% more per month than year one, and so on.
Does it account for inflation?
Optionally. If you enter an inflation rate, the tool also shows the 'real value' — the future balance discounted back to today's purchasing power, which is usually the number that matters for planning.
Is dollar-cost averaging the same as a lump sum?
No. This tool projects a steady monthly plan. Investing a lump sum up front is exposed to the market for longer and historically wins more often in rising markets, while regular investing spreads out your entry. Set the monthly amount to zero and use the initial amount to model a pure lump sum.

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Information tool only. Every result is deterministic arithmetic (for the simulator, a probability estimate) from the numbers you enter. No live data, no account connection, nothing stored. This is not investment, trading, tax, or financial advice — verify against your own broker or prop firm before acting.
Disclosure. Some outbound links may be affiliate or partner links; they never change how a tool computes.
Position Math · updated 2026-06-27 · all calculators
Information tool only — not investment, trading, tax, or financial advice. All computation runs in your browser.