I did find this on the IRS website: (I suspect spiritrider eluded to it) You must make matching and nonelective contributions to the financial institution maintaining the SIMPLE IRA no later than the due date for filing your business's income tax return, including extensions, for the taxable year that includes the last day of the calendar year for which you made the contributions. If you extend your tax return, then you have until the end of that extension period to deposit contributions, regardless of when you file the tax return. However, if you did not deposit the contribution timely, you must amend the tax return and pay any tax, interest and penalties that may apply.