網上寫As long as your Solo 401(k) was setup before December 31s

As long as your Solo 401(k) was setup before December 31st, you may make contributions as an “employer” for the previous year until the IRS tax deadline. 不知道我的情況是否適用，我沒有注冊公司，是用SCHedule C報稅

https://www.sharebuilder401k.com/blog/solo-401k-tax-deadlines-and-how-you-can-minimize-taxes/