When the broker changes the contract size

[Fairman]

When the broker changes the contract size

A lot is 100,000 units, until it isn't. Some brokers define lots differently on certain symbols, or change contract specifications for specific instruments without much notice.

The most common source of confusion is non-forex instruments sharing the platform. Gold might be 100 ounces per lot on one broker and 1 on another. An index CFD might be 1 dollar per point or 10. Oil can differ again.

The change that hurts is a mid-life revision: the broker adjusts the contract size of a symbol, and any script using fixed lot sizes now carries different exposure than before.

Margin requirements follow the contract size, so a change alters the margin used. A position that comfortably fit in the account can suddenly occupy a larger share.

Checking the specification of every instrument at the start of a week, especially after a platform update, costs little. A saved screenshot of the spec for each symbol provides a record to compare against later.

On forex majors, the contract is stable. On everything else, it pays to look rather than assume.

Has a contract size ever differed from what was expected, and what did it cost?