Contribution deadlines vary depending on whether it is a salary deferral or contribution based on profits generated. The contributions to a Self-Employed 401(k)s consist of two parts, and the deadlines for these parts are different.
The contribution which you as an employee make on your own behalf, which is considered a salary deferral, is 15 days after the close of your fiscal tax year. If you have a regular fiscal year, which ends on December 31, the contribution deadline is January 15th. These contributions include both regular salary deferrals and catch-up contributions.
In 2016, these deferrals can be up to 100% of compensation or $18,000 if under 50 years old, and up to $24,000 if you’re over 50. The second part of your contribution comes from the profits you generated. In order to compute these profits, you have to prepare the income tax for your business.
The standard deadline for such income tax is March 15th, and if you are one of those very organized business owners who can do it before the deadline, you still have until March 15th to make the contribution. If, however, you belong to a vast majority of procrastinators and file for an extensions of your business income taxes until, say, August 15th, your contribution from the profits will also be due by that date.
These profit-sharing contributions can only be up to 25% of your net profit/gross income, and it will actually be reduced by an amount including part of the self-employment tax that makes it 20% of your gross income. You’ll want to check with your CPA or custodian company to make sure you’re crunching the numbers right.
In 2016 the profit sharing contributions can be up to $53,000, reduced by the amount of salary deferrals you take (leaving out the catch-up contributions, which can make the account total $59,000).