TL,DR: I want some earned money, a little more than $10k, to be contributory to 2023 income so as we can contribute an additional 2,5k to my SEP. Employer is willing to accommodate as needed. Can an additional paper check be added into a W2 outside of a payroll run? I believe yes, I'll just need to reserve a portion for taxes.

So I'm technically the employee in this example, my parents are the small business.

We're in sales and maintain a consulting arm with 3-4 high level clients. One client was transitioning AP software as they had been through a merger. They were still within their Net 30 terms, but later than we had been expecting, so it missed December payroll. My mom's plan had been to run an additional payroll and zero out the other fields for the other employees and just pass along this payment to me. Her payroll software (Truist) is saying it can't run the payroll with it being a full payroll, which isn't what she wants. So she wants to cut me a check for the value.

I would really like for this to hit my 2023 year so as we are able to contribute 25% towards my SEP.

Worst case scenario, this could wait until January and be contributory to 2024.

I recognize this is an issue with the payroll, so I will look into that. But can anyone speak to if this is possible? To have additional income be paid outside of the payroll system (via a paper check), but still be added into my W2? Again, I do know I need to save a portion for taxes.

1. I want the money to be part of 2023 income, so as we can contribute 25% of income to SEP, even though we're going around payroll.

2. Payroll e-filed W2 will reflect slightly lesser value. I will make sure my accountant knows this additional income should be written in when filing W2. What else do I need to do to show this is income, if anything?

I'm calling my accountant in the morning, but I was hoping I could talk it through on Reddit before then.