Client received money for a commercial lease buyout in 2017. The payment was to change the lease so that the lessor can break the lease with 60 days notice. I know the payment would be considered capital gains however, when is the transaction triggered? In 2017, when the payment was received or when the lease is actually broken?

Client is accrual basis-can the payment go on the balance sheet until the future year that the lease is broken? He will likely close his business rather than relocate and closing would probably net to a loss. Client does not want to pay capital gains now then have a large capital loss in a future year.

I do not yet have the actual paperwork with the terms of the lease buyout...

Thanks for any input/direction!