A transaction (or a type of transaction) that occurs only on a time-to-time basis or periodically, but not as a routine. This involves activities and/ or events that take place only periodically such as taking physical inventory, calculating depreciation expense, and adjusting for foreign exchange translation effects.

Nonroutine transactions are characterized by the fact that the information involved are generally not part of the routine flow of transactions. In other words, this refers to transactions that are unusual, either due to size, nature and reason, and therefore do not occur frequently.

Nonroutine or unusual transactions include, but are not limited to, major property acquisitions (mergers, acquisitions, etc.), asset write-offs, losses due to natural disasters (force majeure), and new product implementation. When recording transactions that occur infrequently, an entity may not have sufficient and adequate experience to establish correct values. In which situation, auditors tend to assume the existence of a high inherent risk. Significant risk usually relates to nonroutine transactions which require special audit consideration.

For example, when an entity acquires a new subsidiary, the transaction and all related accounting treatment and financial reporting processes will be conducted as for any unusual, nonroutine transactions. Acquisition-related expenses arise and are considered nonroutine transaction costs. The same may apply to determining the allowance for doubtful accounts, though in certain cases such a process is more into an accounting estimate transaction. Other examples of nonroutine transactions may include issuance of bonds (debt securities) or additional shares.

Nonroutine transactions may increase the risk of material misstatement because of the great extent of management intervention required, including more reliance on manual data collection and processing. Due to their infrequent nature, such transactions may require complex calculations or unusual accounting principles not subject to effective internal controls.