Ready to offer a 401(k) plan? Know your options: Traditional 401(k)s let employees contribute pretax dollars and give employers the option of matching contributions. But rigorous testing rules apply. Roth 401(k)s allow employees to contribute after-tax dollars and take tax-free withdrawals (subject to limitations). Safe harbor 401(k)s avoid strict testing but require certain employer contributions. Smaller businesses may offer SIMPLE 401(k)s, which are akin to safe harbor plans but have lower required employer contributions and employee contribution limits.