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SIP or ETF Savings Plan? How Monthly Investing Actually Grows

Written by ZixoTools Team
October 18, 2026

In India it is called a SIP, a systematic investment plan. In Germany it is an ETF-Sparplan. In the UK people talk about drip-feeding into a Stocks and Shares ISA. The names differ, but the idea is the same everywhere: invest a fixed amount every month, automatically, and let compounding do the heavy lifting.

How the growth is calculated

Each monthly instalment grows for the months left until the end of the plan. The first instalment compounds for the whole term, the last one for a single month. Adding all of those up gives the future value:

FV = P × ((1 + i)ⁿ − 1) ÷ i × (1 + i)

Here P is the monthly amount, i the monthly return (the annual rate divided by 12) and n the number of months. The final (1 + i) assumes you invest at the start of each month.

What 200 a month becomes

Assume 200 a month (euros, pounds or dollars — the maths does not care) and a 7% average annual return, a common long-run assumption for a global equity ETF.

  • 10 years: you put in 24,000 and end with about 34,800.
  • 20 years: you put in 48,000 and end with about 104,800.
  • 30 years: you put in 72,000 and end with about 245,400.

Look at the gap between 20 and 30 years. Ten more years of the same 200 a month adds 24,000 of your own money but about 140,000 of value. Most of the growth arrives late, which is why starting early matters more than almost anything else.

Doubling the amount is not the same as doubling the time. 400 a month for 10 years also means putting in 48,000, but it grows to about 69,600, not 104,800. Same money, ten fewer years of compounding.

The same plan in rupees

The classic Indian example is ₹25,000 a month for 10 years at an assumed 12%. You invest ₹30 lakh and end with roughly ₹58 lakh. Equity mutual fund returns are often modelled at 10–12%, but that is an assumption, not a promise.

What taxes take out

The calculator shows gross figures. Tax depends on where you live, and it is worth knowing the broad shape:

  • Germany: gains are taxed at the flat Abgeltungsteuer of 25% plus solidarity surcharge (26.375% in total, more with church tax). Equity ETFs get a 30% partial exemption (Teilfreistellung), so the effective rate on gains is about 18.5%. Each person has a €1,000 annual saver's allowance (Sparer-Pauschbetrag). A small advance lump-sum tax (Vorabpauschale) can apply to accumulating ETFs each January.
  • India: long-term capital gains on equity funds held over a year are taxed at 12.5% above an annual exemption of ₹1.25 lakh.
  • UK: investing inside a Stocks and Shares ISA, up to £20,000 a year, keeps the gains free of tax.

Rules change, so check the current position for your country before relying on a figure.

Fees matter more than they look

A fund costing 0.2% a year and one costing 1.5% a year look similar on paper. Over 30 years the difference compounds into tens of thousands. Broad index ETFs and direct mutual fund plans tend to be the cheapest route, and many brokers now offer free savings plans.

The return you assume changes everything

At 5% a year, 200 a month for 20 years grows to about 82,000 rather than 104,800. At 9% it is closer to 135,000. Run the plan at a cautious rate and treat anything above it as a bonus. Returns are not smooth either: some years will be negative, and the plan only works if you keep paying in through them.

Run your own plan

Enter your monthly amount, expected return and time frame in the SIP calculator. It works the same for an ETF savings plan in any currency. To see how a lump sum compares, use the compound interest calculator, and the inflation calculator shows what the final figure is worth in today's money.