This article relies largely or entirely on a single source. (January 2020)
When trading in bonds, accretion is the capital gain expected when a bond is bought at a discount to its par value, given that it is expected to mature at par. Accretion can be thought of as the antonym of amortization: see here also, Accreting swap vs Amortising swap.
In a corporate finance context, accretion is essentially the actual value created after a particular transaction. A deal is earnings accretive if the acquirer's price-to-earnings ratio is greater than the target's price-to-earnings ratio, including the acquisition premium. Similarity, re mergers and acquisitions, accretion is referred to as the increase in a company's earnings per share on a pro forma basis following the transaction. (For example, if Company A has $1.00 earnings per share and after acquiring Company B, the combined company's earnings per share is $1.25, then the acquisition would be referred to as 25% accretive.) By contrast, a transaction is dilutive where the earnings per share decreases following the transaction. See: Accretion/dilution analysis, Diluted EPS, Dilutive security; Swap ratio.
In accounting, an accretion expense is created when updating the present value of an instrument. (For example, if you originally recognize the present value of a liability at $650, which has a future value of $1000, every year you must increase the PV of the liability as it comes closer to its FV. If the above liability, for example an asset retirement obligation, had a discount rate of 10%, accretion expense in Yr.1 would be $65 and the PV of the liability at the end of Yr.1 would be $715.) Since the statement dates will not necessarily coincide with the anniversary dates of these commitments, the expense is prorated.