What the previous close is
The previous close is the last price recorded for an asset before its most recent session ended. For a market with defined trading hours, that is the official closing price of the prior day. Once the session closes the value is fixed as a reference, and it does not change during the next session even as the live price moves.
Why the previous close matters
Most measures of daily performance are calculated against the previous close. The day's change is the current price minus the previous close, and the percentage change expresses that difference relative to it. For this reason the previous close is the anchor for the gain or loss figure shown next to most quotes and for the reference line drawn on an intraday chart.
Closing price in 24-hour markets
Markets such as crypto and spot currencies trade continuously and have no natural close. For these, a previous close is defined by a daily cutoff time, for example the price at a fixed UTC hour. The cutoff is a convention rather than a market event, so different providers can report slightly different previous-close values for the same continuous market depending on the cutoff they use.
Gaps between close and open
While a market is closed, news and activity can still shift expectations, so the next session may open at a different price from the previous close. That difference is the opening gap. A large gap indicates significant movement while the market was closed, and it is measured precisely because the previous close provides a fixed point to compare the open against.
Previous close on SiftingIO
SiftingIO provides the data required to derive the previous close and the daily change across stocks, forex, crypto, and commodities under one schema. Historical OHLCV bars over REST supply each session's close, and the live feed over WebSocket supplies the current price, so the day's change can be computed consistently in every market. For continuously trading markets, documented conventions keep the values aligned.