Is there a NAICS code already assigned to my LLC somewhere, or do I just pick one myself?

Nobody assigned your LLC a NAICS code. You pick it yourself when you register in SAM.gov, and the IRS, your state and the EIN letter don't hand one out.

The business activity code on your tax return comes from the IRS's own list, which is built off NAICS, so it's a decent starting point. It isn't binding, though. A few of the firms I do SAM renewals for filed taxes under one code years ago and now list a different primary in SAM because their work changed.

Here's how I walk clients through it:

• Search the Census Bureau's NAICS lookup by what you actually invoice for, not what your business name sounds like.
• Pick one primary and add every secondary code you'd realistically bid under. SAM lets you list several.
• Check each code against the SBA size standards table in 13 CFR 121.201, since SAM shows you as small or not small per code.
• Read solicitations you want to win. Under FAR 19.102 the contracting officer assigns the NAICS code to each buy, so if your targets keep using a code you didn't list, add it at your next update.

A different code on your state filing won't break anything. SAM.gov doesn't pull NAICS from your state paperwork. Just keep your state vendor portal profile matched to the work you really do, because buyers there search by commodity code too.

The NAICS code you select for your SAM.gov registration is critical because it dictates the small business size standard applied to your firm for federal contracts. The SBA size standards are set by NAICS code and are expressed either in number of employees or in annual receipts in millions of dollars (13 CFR 121.101 and 121.201). When you bid on a contract, the contracting officer will assign a NAICS code to that specific solicitation, and your eligibility as a small business for that award will be determined by comparing your firm's size against the standard for the assigned NAICS code. If your registered primary NAICS code in SAM.gov doesn't match the solicitation's NAICS code, you may still be considered a small business if the solicitation's code is also listed in your SAM.gov profile and you meet its size standard.