Editorial
This article explains how trading units (round lots) work and how buying less than one unit differs, using hypothetical numbers.
Contents
Many people who look into buying shares for the first time discover that the minimum purchase can seem large. The reason is that stocks are traded in a standard block called a trading unit, or round lot. This article explains how units work, how buying less than one unit differs, and what to check beforehand. All figures are hypothetical illustrations and do not refer to any particular company or service.
What a trading unit is
A trading unit is the number of shares that serves as the basis for trading on the exchange and for counting voting rights. Each listed company sets its own unit size. In Japan, a unit of 100 shares is common today, but because the size is set company by company, it should be confirmed in the company’s own disclosures before buying.
In ordinary exchange trading, one unit, or a whole multiple of it, is the smallest amount you can trade. The money required is therefore the share price multiplied by the unit size.
Suppose a share costs 2,000 yen and one unit is 100 shares. The required amount is 2,000 yen x 100 = 200,000 yen. If the price were 5,000 yen, the amount would be 500,000 yen (5,000 x 100). The higher the share price, the larger the initial amount needed.
Buying in small amounts: fractional shares
Some brokerages let customers trade fewer shares than one unit. Whether this is offered, which stocks are covered, how many shares can be bought, and what it costs all vary by firm and by service.
Using the same example (2,000 yen per share, 100 shares per unit), buying just 10 shares takes 2,000 x 10 = 20,000 yen, compared with 200,000 yen for a full unit. The money can be started in smaller pieces.
Some firms also let customers specify a yen amount instead of a share count. In that case the firm buys the number of shares that comes closest to the amount. The mechanics differ from firm to firm, so the terms of service and trading rules are worth reading.
How the two approaches differ
| Item | Full unit | Less than one unit |
|---|---|---|
| Quantity you can buy | Whole multiples of one unit | From one share or a similar small amount |
| Money required | Price x unit size | Price x shares bought |
| Voting rights | One vote per unit | Usually cannot be exercised |
| Dividends | Paid in proportion to shares held | Paid in proportion to shares held |
| Shareholder perks | Eligible if conditions are met | Often not eligible |
| How trades happen | Real-time on the exchange | By the firm’s own method and schedule |
Dividends are normally proportional to the number of shares. If a company pays a hypothetical 40 yen per share per year, 10 shares would receive 400 yen (40 x 10) and 100 shares would receive 4,000 yen (40 x 100). Dividends are not fixed, and a company may raise, cut, or skip them depending on results and policy.
One more practical difference is how a position can be changed later. A holder of full units can sell part of a position on the exchange at a price they specify, while a holder of fractional shares may need to use the firm’s own sell method. Some firms also allow fractional holdings to be topped up to a full unit, after which the holding behaves like an ordinary one. Because these arrangements are set by each firm rather than by a common rule, it is worth reading how selling works before the first purchase, not after.
Points to check before buying
- Timing of execution: Unlike full-unit orders that can fill during market hours, fractional orders at some firms are batched at set times. The price you saw when ordering may differ from the execution price.
- Fees and spreads: Even when commissions are zero, a firm may set a gap between its buy and sell prices. On small trades, that gap can look large as a percentage.
- Order types: The kinds of orders available, such as limit orders, may be more limited than for full units.
- Perks and voting: Shareholder perks often require a minimum number of shares, so holdings below one unit may not qualify.
- Accounts and taxes: Whether fractional shares can be held in a particular account type, including tax-advantaged accounts, depends on the firm.
Here is a hypothetical cost illustration. If you spend 20,000 yen on a trade and the effective cost from the buy-sell gap is 1%, the cost is 200 yen (20,000 x 1%). The yen amount is small for a small trade, but it accumulates as the number of trades grows. Check the actual terms on each firm’s information pages.
Using small purchases in practice
Being able to buy small amounts fits well with spreading purchases over time rather than investing everything at once. To see how regular monthly purchases can work under different amounts and periods, you can try the dollar-cost averaging simulator (Japanese).
That said, small amounts are not a reason to concentrate on one stock. Splitting a small budget across many stocks makes each purchase even smaller, which can increase the relative weight of fees and spreads. For how this site handles its content, see the editorial policy.
Points to consider and risks
Fractional shares lower the financial barrier to getting started. They do not change the price risk of the stock itself. Share prices can fall, and the value can end up below the amount invested. A small amount means a small maximum loss in yen terms, not an absence of risk.
Fractional holdings also come with trade-offs: no voting rights, possible exclusion from perks, restrictions on how orders are placed, and a limited number of firms that offer them. It helps to weigh these constraints alongside the convenience and decide whether they fit your own purpose.
Before buying, it is sensible to secure living expenses and an emergency fund, and to invest only an amount whose loss would not cause immediate hardship. For the latest rules on taxes and systems, check official sources such as the Financial Services Agency and the National Tax Agency, along with each firm’s guidance. See also the disclaimer for the limits of this content.
About this article: This is a basic guide article. Our policy is to check the content against public sources. It is not investment advice. If you notice an error, please contact us.