The terms T+1, T+2, etc., are a shorthand for "trade date plus one day", "trade date plus two days", etc., indicating how many business days after a security transaction occurs that the trade must be settled. Rules or customs in financial markets for securities transactions provide for this 'settlement period', which is the mandated time for official transfer of securities to the buyer's account and the cash to seller's account. Following that cycle has been titled the regular way or a regular way contract.

The most common current settlement period for securities transactions is one business day after the day of a transaction, which is abbreviated to T+1. On settlement, the seller must produce the security's certificate and executed share transfer form in exchange for payment from the purchaser. Many countries now dispense with the requirement that a physical stock certificate be produced, a process known as dematerialization, and have adopted electronic settlement systems.

During the 1700s the Amsterdam Stock Exchange had close links with the London Stock Exchange and they would often list each other's stocks. To clear the trades, time was required for the physical stock certificate or cash to move from Amsterdam to London and back. This led to a standard settlement period of 14 days which was the time it usually took for a courier to make the journey on horseback and by ship. Most exchanges continued to use the same model over the next few hundred years.

Settlement procedures varied considerably across national stock markets. There were two main types of settlement period used by different countries, either a fixed number of days after the transaction known as fixed settlement lag or periodically on a fixed date when all transactions up to that date are settled known as fixed settlement date. In France, Italy, and, to some extent, Switzerland and Belgium, as well as some developing countries, the settlement of all transactions took place once a month on a fixed date. This system was instituted by Napoleon.

The last day of trading on which all trades are settled was called the liquidation. The liquidation took place on the seventh business day preceding the end of the calendar month.

In the United States, the New York Stock Exchange used T+1 in the 1920s, and the American Stock Exchange used T+2 prior to 1953. These settlement periods were gradually extended to T+5 by the late 1960s as brokerage firms became overwhelmed by the massive volume of securities transactions paperwork awaiting settlement.

The Black Monday (1987) stock market crash prompted a move to reduce settlement times. Settlement dates in most exchanges reduced to three days (T+3).

In 2017, the move by most stock exchanges was towards adoption of T+2 (trade date plus two days). For example, the United Kingdom adopted T+2 in October 2014 and the United States adopted T+2 in September 2017.

Indian stock exchanges planned a move to T+1 starting in 2022. The US and Canada targeted a transition to T+1 early in 2024. Canada adopted T+1 beginning on May 27, 2024, as did Argentina, Jamaica, Mexico, and the US on the following day. Chile, Colombia, and Peru are slated to move to T+1 in 2025, and ESMA recommended the EU transition to T+1 on October 11, 2027.