Here is some general SEP IRA information, please do not forget about the contribution deadline for 2015. Generally a SEP must be established and funded by your tax filing deadline. Generally, filing extensions extends the period for establishing and funding the SEP plan. For a sole proprietor April 15th would be the deadline to establish and fund a SEP for the prior tax year. If an extension was filed a sole proprietor can establish and fund a SEP IRA by October 15th.