Personal finance
Regular monthly investment plan calculator
Enter what you put in at the start and every month, for how many years and at what expected return: see what you could have at the end, how much you paid in, what the fees cost and how much tax takes.
How a regular investment plan works
A regular investment plan puts a fixed sum into the market at regular intervals, usually every month. It enters the market bit by bit: when prices are low it buys more units, when they are high fewer. It is the simplest way to invest savings that arrive every month from a salary.
The engine is compound interest: each year's gains earn further gains in the years that follow. With 1,000 at the start and 150 a month for 20 years, at 5% a year and a 0.2% TER, you pay in 37,000 and could end up with about 62,000, or about 55,500 after a 26% tax on the gain.
Costs look small but they compound too: in the example the 0.2% a year costs about 1,500 over twenty years, and a fund charging 2% would cost far more. That is why, for the same exposure, low-cost ETFs are often the most efficient choice.
Common mistakes
- Using an expected return that is too high: a few points of difference change the result enormously over twenty years.
- Ignoring annual costs: a 1.5% TER instead of 0.2% can eat a fifth of the gain.
- Stopping the plan when markets fall: that is exactly when contributions buy the most units.
Frequently asked questions
Is a monthly plan better than investing everything at once?
Statistically, investing a sum you already have at once earns more, because markets rise more often than they fall. A monthly plan is the natural choice for investing savings as they arrive, and it lowers the risk of going in at the worst moment.
What return can I expect?
Nobody can guarantee it. Historically a global equity portfolio returned 5 to 7% a year nominal on average over long periods, with some very negative years; a bond portfolio less, with smaller swings.
When is tax paid?
In most countries tax on fund gains is due when you sell, not while the plan builds up, which is why the simulation applies it only at the end. Tax-free accounts avoid it altogether.
How this calculation works
Monthly growth = (1 + annual return)^(1/12) × (1 − TER)^(1/12). Each month: value = value × monthly growth + contribution × (1 − fee). Gross gain = final value − capital paid in; tax = gain × rate if positive; net value = final value − tax. Cost of fees = value of the same plan without costs − value with costs.
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Solve for capital, rate, periods or final amount using the compound interest formula.