Wealth accumulation with UCITS ETFs: what the monthly contribution actually does

Three things decide what a monthly ETF plan is worth in thirty years. How much you put in, how long you leave it alone, and what the market pays while you wait. You set two of them.

Take €300 a month, a 7% annual return and a thirty-year horizon. You pay in €108.000 across 360 transfers. The projection finishes at €350.836, so €242.836 of the final balance was produced by the plan rather than by you.

That growth arrives late and it arrives unevenly. Knowing when it arrives is most of what separates an investor who keeps the plan running from one who concludes in year six that it is not working.

The 7% is an assumption and not a forecast. Nobody knows what the next thirty years pay, and this guide makes no claim about it. What arithmetic can settle is which of the three inputs moves the answer most, and the winner is the one you write on a standing order.

Contributions are a straight line. €300 a month is €3.600 a year, in year one and in year thirty alike. Growth is not a straight line, and the gap between the two shapes is the entire subject.

For the first eighteen years of that plan, more of the balance is money you paid in than money the plan made. In year nineteen the two cross over, and the gap widens from there.

Hold the base case still and improve one input at a time. Thirty years, a zero opening balance, 7% a year, €300 a month, ending at €350.836.

Raise the contribution to €400 a month and the plan finishes at €467.781. That is €116.945 more, bought with €36.000 of additional transfers spread over three decades.

Leave the contribution at €300 and raise the return to 8% instead. The plan finishes at €422.565, which is €71.729 more.

One extra percentage point a year, sustained for thirty years, is a spectacular investment result. It is beaten here by a hundred euros a month, and the two are not equally available. The transfer is a decision you make once in an app. The percentage point is something you can hope for and cannot arrange.

Most writing about ETF investing, this site included, is about the second number. Which index, which provider, three basis points of ongoing charge. That work is finite and its ceiling is lower than the contribution's.

One part of the return is genuinely yours to set, and it is the reason the fee gets a section of its own below. A charge is subtracted with total reliability in every year, good or bad, which makes it the one component of the return that behaves like a decision rather than like weather.

A ten-year delay does not cost you the first decade's €51.316. It costs the last decade's €198.575, because every year you remove comes off the end of the plan, where the balance is at its largest.

Run the same €300 a month for twenty years instead of thirty and it finishes at €152.261. The ten years skipped at the beginning are the ten that were going to do 57% of the work.

Everything above assumes a contribution arrives every month for three decades. This section is about making that assumption true, which is a problem of plumbing and temperament, not of markets.

A broker savings plan is a standing instruction to buy a fixed euro amount of a named fund on a fixed day each month. Most European brokers offer them, often at a reduced commission or none, and they deal in fractional units so the whole €300 goes in instead of the largest whole number of units that fits underneath it.

A standing instruction also removes the monthly decision about whether now is a good moment to buy. That decision is the mechanism by which plans quietly stop, and the mechanics of the purchase itself are identical whether a human or a schedule triggers it.

A thirty-year accumulation plan wants its reinvestment to happen without being asked. An accumulating share class does exactly that. Dividends paid by the companies in the index are reinvested inside the fund, at institutional dealing costs, on a scale where commission is a rounding error.

A distributing class hands you the cash instead, and you reinvest it by hand. Early in a €300 monthly plan those payments are a few euros at a time, and paying a €3 commission to reinvest €8 gives more than a third of it away. Letting the cash sit uninvested instead costs little over weeks and stops being little over a year.

Which class suits you is a tax question before it is a mechanical one, and the answer turns on which of three shapes your country's fund taxation takes. Settle it before the first purchase, because switching later means selling, which in several countries is the taxable event you were trying to defer.

The UCITS label underneath all of this promises something narrower than its reputation suggests. It sets rules about diversification, custody and your right to redeem. It says nothing about whether the fund is cheap, whether the index is sensible, or whether you will make money. For a thirty-year plan the custody and redemption rules are the part that matters, because they are what the wrapper still owes you during the decade you most want to stop reading about it.

Three things come out of the number in the projection. The fund charges one, your own country takes the second, and the third arrives without anybody collecting it.

A fund charging 0,60% a year takes €36.507 out of the thirty-year plan above. Of that, €18.756 is money deducted from the fund and handed over. The other €17.751 is the growth that deducted money would have produced had it stayed invested. Which half dominates depends on the horizon and not on the fee, running at roughly an eighth of the damage at five years and two thirds at fifty.

The same plan in a fund charging 0,20% loses €12.668. The gap between the two funds is €23.839, or about 22% of everything you paid in over thirty years, for a difference that looks like four tenths of one per cent on a fact sheet. The headline fee is not the number that decides what you keep, so compare tracking difference before treating the cheaper ongoing charge as settled.

The second deduction is your own tax authority, and this site publishes no national rates because fund taxation is amended more often than articles are rewritten. What is stable is the structure. Three separate layers take a share of an index fund's return, only the last of which sends you anything to read, and over thirty years the compounding cost of the annual ones works exactly like the fee above.

The third deduction has no recipient. At 2% inflation, €350.836 in thirty years buys what €193.686 buys today. The euros are all still there and what they buy is 55% of what the same figure buys now, so the compound interest calculator restates every projection at current prices beside the nominal one.

A calculator that applies 7% in every one of thirty years is describing a market that has never existed. A real period averaging 7% contains years of +25% and years of −40%, and the average is only visible from the far end.

That matters more than it looks, because the order matters once contributions are involved. A bad decade at the start of a plan hits a small balance and buys the following years cheaply. The identical decade at the end hits the largest balance the plan will ever hold, with no time left to recover. Two investors can live through the same thirty years in a different order and finish in different places.

This is sequence-of-returns risk, and no constant-rate model can show it. Every calculator page on this site says so in its assumptions panel for that reason, alongside the fact that tax and trading costs sit outside the model too.

None of that makes the projection useless. It makes it a device for comparing plans against each other, which is what it is good at. €300 against €400 a month, twenty years against thirty, 0,20% against 0,60%: those comparisons hold no matter what the market does, because the same wrong assumption sits on both sides of them.

The other direction is often the more useful one. Instead of asking what €300 a month becomes, name the amount you want and let the arithmetic price it.

Reaching €500.000 at 7% from a standing start costs €292 a month over thirty-five years, €428 over thirty, €639 over twenty-five and €985 over twenty. Shortening the horizon from thirty-five years to twenty multiplies the monthly cost by more than three, and the money the plan is no longer making has to come from somewhere.

The same effect shows up as milestones. On €300 a month, the first €100.000 takes about as long as the following three hundred thousand combined.

Seven that come up almost every time somebody starts one.