I have a client that is a hair dresser. She files a schedule C every year. Sole proprietorship. Her net profit on schedule C is usually in the $35,000-$50,000 range. She has never setup a self employed retirement plan. Can she open a solo/individual 401(k) now and still make 2023 employee (up to $30,000) and 2023 employer contributions (to be calculated by accountant)? I know typically employee contributions have to be made by year-end but I think recent tax law changes allow for those that file a schedule C to make prior year employee solo 401(k) contributions up until the tax filing deadline. Is this correct?

Assuming she can still make 2023 employee and employer contributions, she will probably put her $30,000 employee contribution as Roth. Due to Secure Act 2.0 can the employer contribution also go in Roth or does that still need to be pre-tax?