US equities, ETFs and corporate bonds moved to t-plus-one in May 2024; several other markets remain at T+2, and some instruments settle same day. Options settle T+1, spot FX conventionally T+2.
Shorter cycles cut counterparty and clearing risk, but compress the time available for funding, foreign exchange and error correction — which is why cross-border managers found the change operationally painful.
Example: buy on Monday under T+1 and cash leaves on Tuesday. In a cash-account, proceeds from a Monday sale are available to withdraw on Tuesday; using them to buy again on Monday is fine, but selling that new position before Tuesday is a good-faith-violation.
Related: t-plus-one, unsettled-funds, good-faith-violation, free-riding