Stock order types: reading your app's buy screen

A stock order is the instruction you give an intermediary to buy or sell a security, with a quantity, a price you accept and a period of validity. In an app, all of it fits on one screen and one button. Yet the words on that screen decide the price you pay, sometimes more than the fees on display.

What is a stock order?

An instruction, not a purchase. Until someone on the other side accepts your price, nothing is executed, which is why the screen asks you for four things: the security, the quantity or the amount, the order type and its validity.

Wikifin, the financial education site run by the FSMA (Belgium's financial markets regulator), distinguishes only two families: the order without a limit, where you want to buy or sell "at the price of the moment", and the order with a limit. Everything else derives from those two.

The eleven words on the buy screen

Figures checked on 6 October 2026: Wikifin, help pages of Trade Republic, Revolut and Bolero, the consumer organisation Test-Achats (4 and 15 September 2026), Curvo (29 June 2026).

Market order or limit order: which one should you pick?

A market order guarantees execution, not the price. A limit order guarantees the price, not execution.

Take an ETF showing 104.20 euros. You want ten units, one evening around 9 pm, on a venue that is still quoting. The gap between buyers and sellers has widened because the reference exchange is closed, and your market order goes at 104.65 euros. Forty-five cents per unit, 4.50 euros in total: that is more than four orders at 1 euro each, and no fee line flags it. The same order with a limit at 104.20 euros would have stayed pending, then been filled the next morning or not at all. Wikifin puts it bluntly: with an order without a limit "you are taking risks", and an unrealistic limit will never be executed.

On a heavily traded ETF, in the middle of the day, the difference is counted in cents.

What is a stop order for?

Selling without watching the screen. You set a trigger below the current price; if it is hit, the order goes. At Bolero as at Revolut, it then becomes a market order, so with no price guarantee whatsoever.

Placing your first order in six steps

1. Check the security by its ISIN code, not its name: two ETFs with similar names can fall under two different TOB rates.
2. Look at the time. A European ETF trades during the day; at Revolut, an order on a US stock placed outside the session waits for the 15:30 open, Belgian time.
3. Choose the order type. Above a few hundred euros, or in the evening, a limit costs you ten seconds.
4. Set the validity: the same day if you are in front of the screen, longer if you are aiming for a price.
5. Read the summary before confirming: fees, estimated amount, and the tax line if the app withholds it.
6. Keep the execution confirmation. You need it for the TOB and for any dispute.

I went back through this on 6 October using the help pages of four of the intermediaries named here, because price lists move: since 5 October Revolut charges a flat 1 euro per order in place of its 0.25% commission, and on 24 November it will remove the free monthly orders from its Standard and Plus plans, according to Test-Achats.

How much does a 100-euro order cost?

A flat fee weighs more the smaller the order.

The weight columns are my own calculation. The TOB comes on top everywhere: 0.12 euros on 100 euros for an ETF taxed at 0.12%, 1.32 euros if it is taxed at 1.32%. Bolero, DEGIRO and Trade Republic's Belgian account withhold it; Revolut's securities account sits with Revolut Securities Europe UAB, in Lithuania, and the tax remains yours to declare, according to Test-Achats. The procedure is in our article on the Belgian stock exchange tax.

One reservation on Bolero, the online broker of the Belgian bank KBC: its help page advertises fees "from 2.50 euros" and refers to a PDF price list that I was unable to open. The brackets therefore come from Test-Achats. As for bunq, its help page states that securities go through its partner Ginmon and are held with Upvest Securities, under the supervision of the German regulator, but it describes no order type at all.

Can you buy a fraction of a share?

Yes, and that is what lets you put 25 euros into a security worth 180: you receive 0.1389 of a share. But it is not a share. Wikifin describes two legal structures, the derivative contract or co-ownership, and spells out what follows: no voting right you can exercise directly, and fractions that can only be sold back to the intermediary that sold them. Test-Achats adds, in its April 2026 report, that they cannot be transferred to another institution and that a market order is often the only type on offer.

So the limit you have just learned to set disappears when you buy by amount instead of by number of units.

Which mistakes should you avoid on a first order?

• Confirming a market order in the evening or at the weekend on a thinly traded security.
• Mistaking the displayed price for the execution price.
• Setting a limit far below the market, then forgetting the order for 360 days.
• Believing a savings plan escapes the tax.
• Stacking 20-euro orders with flat fees: five orders at 1 euro on 100 euros make 5% in fees.
• Thinking a stop protects you from a sharp drop at the open.

In short

Four settings are enough for a first order: the right ISIN code, a time when the market is open, a limit as soon as the amount matters, a validity you chose. Flat 1-euro fees have made small orders affordable, and savings plans make them free at several players; what remains is the Belgian tax, which only some of the apps collect. To find out which entity holds your securities and what protection applies, see our article on the difference between an e-money institution and a bank, then the details of the Trade Republic offer in Belgium. The comparator lines up the current accounts that feed those investments.

This article explains vocabulary and fees; it recommends no security and is neither investment advice nor tax advice.

Sources: Wikifin (FSMA), "Comment vendre et acheter des actions ?", "Les investissements fractionnés" and "Comment investir dans un tracker et combien ça coûte ?", consulted on 6 October 2026; directive 2009/65/EC; Test-Achats, articles of 4 and 15 September 2026 on brokerage fees, Trade Republic and Revolut's pricing, and April 2026 report on fractional investing; Curvo, "DEGIRO costs for ETFs", 29 June 2026; help pages of Trade Republic, Revolut, Bolero and bunq, consulted on 6 October 2026.