IAAL. In fact IAATL. In fact I have prepared hundreds of tax returns and am currently defending dozens of innocent Swiss bank accounts from the greedy clutches of the IRS. </STFU, Phil> But I digress.
Here are some scenarios.
1. You really truly have zero income.
In that case file an income tax return. You do not have a filing obligation but do it anyway. The IRS has a three year window to audit you. This time starts from the moment you file a tax return. So file the tax return and get the clock ticking.
This is a "stick the pacifier in the baby's mouth" theory of tax returns. The IRS will get noisy and send you letters asking why there is a gap in the sequence of filing tax returns. Prevent that.
Since the 3 year clock doesn't start until you file a tax return, imagine 7 years from now when you are a Bloated Plutocrat the IRS comes to audit you. They say "Hey, what about 2010? No tax return! We gotcha!" You say "But I didn't earn anything in 2010." They say "Prove it." You say, "Meh, I threw away all my paperwork for 2010 because I asked about electronic filing of financial records on HN and I got a comment back that said to never save anything."
You. Are. Dead.
Memo to all personnel: file the tax return, even if you lived on the beach and ate abalone you caught all by yourself and walked around naked.
2. You earned money but not a lot, so you don't owe any tax.
This is the scenario where you make a couple of thousand dollars, but below whatever the personal exemption + standard deduction is for that year. Even if you fully report everything, you won't owe any tax.
Again, file the damn tax return. It starts the clock running on the 3 year audit window. It prevents you attempting to reconstruct the past if the IRS does come back at you later.
This is especially true if you have a 1099 in any amount. You will get dunning letters from the IRS.
So do it.
3. You earn some money but you have deductible expenses and other losses that mean you owe no tax.
You can predict what I'm going to say. File. Start the clock running. Get your deductible expenses and losses documented.
4. Backing up a step.
I have handled audits where people have reported small amounts of income on their tax returns and the audit is triggered on a simple, common-sense question from the IRS computers: "Well, how did he eat and pay rent?"
Be prepared to document that you drew down from savings. It will work and work well as a defense on the audit.
5. I am assuming your startup is not incorporated.
There you are. Have at it. Question time! Hit me with some.