I'm an S corp employee owner (no other employees) trying to enter employee + employer 401k contributions made by my corp through the year. How to do this in QB payroll?

I see you are trying to enter employee plus employer 401k contributions made by your corp throughout the year in QuickBooks Online Payroll. Worry not. I've got you covered. I have here guidelines to help you record these contributions in your QBO account.

You can set up a payroll item for 401K to record both employee and company contributions within QuickBooks Online (QBO) Payroll. After processing a payroll, this will automatically log the deductions in your bank account. Here's the process:

1. Go to Payroll, then select Employees.
2. Click the name of your employee and select the Pay pencil icon.
3. Go to Does employee have any deductions? section and click + Add/edit deductions.
4. Select + Add/edit deductions/contribution.
5. From the Deduction/contribution ▼ drop-down list, choose + Add deduction/contribution.
6. Select a Deduction/contribution type and Type. 
7. Add a Description. This is the deduction or plan name which appears on paychecks.
8. Choose whether you want the deduction to be calculated as a Flat amount or Percentage of gross pay. Then enter the amount or percentage. 
9. Click Save, then Done.

For additional details, including instructions on allocating retirement plan deductions and company contributions, refer to this article: Set up or change a retirement plan.

With all that, you can enter employee plus employer 401k contributions made by your corp throughout the year in QuickBooks Online Payroll. Drop me a comment below if you have further questions about setting up 401k or other QuickBooks-related concerns. I'll be happy to help you some more. Have a great day ahead!