Post Filing Business Retirement

[Esalfi]

Is it possible to amend a business tax return if it was filed by 3/15 to add a retirement plan contribution to a defined benefit plan.  

the plan has not been established by the client was to make contribution and amend the tax return 

[dmertz]

Since the business is not a sole proprietorship, the deadline to establish the plan was December 31 of the corresponding tax year.

See Setting up a Qualified Plan in IRS Pub 560:  https://www.irs.gov/pub/irs-pdf/p560.pdf