Trading Day
A day the exchange is actually open for trading, with weekends and holidays excluded — of which there are about 252 in a year.
A trading day is any day the stock exchange is actually open. Markets close on weekends and public holidays, so while a calendar year has 365 days, only about 252 of them are days when stocks actually change hands. That is why finance tends to count time in trading days rather than calendar days.
LDBD measures how long a prediction is held in trading days too. A week is five trading days, a month is twenty-one, and a year is 252. Since prices do not move while the market is closed, counting only the open days gives a cleaner basis for comparing how predictions performed.
Example
With roughly 252 trading days in a year, a one-day prediction's holding period works out to 1/252 of a year, about 0.004.
How LDBD uses it
When LDBD annualizes predictions across different timeframes to rank them on one scale, it converts each holding period into years using trading days: a one-day call is 1/252 of a year, a week is 5/252, a month is 21/252, and a year is 252/252 = 1. It divides the directional log return by that figure to get an annual rate. Trading days follow the NYSE/NASDAQ calendar for US assets and the KRX calendar for Korea, with temporary closures patched in through a holiday_overrides table.
FAQ
How is a trading day different from a calendar day?
A calendar day is every day, weekends and holidays included; a trading day counts only the days the exchange was actually open. A week is seven calendar days but usually five trading days.