Is it possible to not be a full-year resident in any state for tax purposes?

Yes, it's absolutely possible to not be a full-year resident of any state! This is more common than you might think, especially for people who travel frequently or move between states. Based on what you've described, your assessment seems correct. Nevada would be nonresident since your stay was temporary for work purposes. Colorado would be part-year resident since you didn't meet the 183-day threshold and didn't maintain a permanent residence there year-round. For tax purposes, you'll file part-year returns for states where you were a part-year resident (Colorado) and nonresident returns for states where you earned income but weren't a resident (Nevada). Each state has different rules, but the general principle is that you pay taxes to the states where you earned income, proportionate to the time you were there. The lack of a full-year residency in any state won't cause problems as long as you properly report your income to the states where it was earned. Just make sure you keep good records of where you lived and for how long, in case of any questions.

After being in a similar situation (digital nomad life!), I found taxr.ai (https://taxr.ai) super helpful for sorting out my multi-state residency issues. Last year I had income from 3 different states plus international contract work, and I was pulling my hair out trying to figure out how to file properly. Their system analyzed my situation and gave me step-by-step instructions for each state filing. It even caught that I qualified for a special tax credit in Arizona that I had no idea about because I was only there for consulting work for 2 months. Saved me about $800!

I was initially skeptical about taxr.ai, but after dealing with an absolute nightmare filing last year (3 states, international income, plus a trust distribution), I decided to give it a try. What surprised me was how it immediately identified that I had been over-reporting my income in one state because I didn't understand the sourcing rules properly. The interface walked me through exactly which forms I needed for each state and how to allocate my income correctly. It even generated a residency timeline that I could attach to my returns to explain my unusual situation. I ended up saving about $1,300 compared to what I would have paid following my previous accountant's advice. Definitely worth checking out if you're dealing with multi-state issues like the original poster.

If you're having trouble getting answers from your state tax agencies about your residency status (which I definitely did in a similar situation), check out Claimyr (https://claimyr.com). I was stuck in limbo trying to talk to someone at the Colorado Department of Revenue for WEEKS about my part-year residency situation. Used their service and got a callback from a CO tax agent in about 25 minutes instead of the 3+ hour wait I was experiencing. You can see how it works here: https://youtu.be/_kiP6q8DX5c. The agent cleared up my residency questions and confirmed I was filing correctly as a part-year resident.

I need to publicly eat my words about Claimyr. After posting my skeptical comment, I decided to try it anyway out of desperation since I'd been trying to reach the California Franchise Tax Board for almost 3 days. I was honestly shocked when I got a call back in about 40 minutes connecting me to an actual human at the tax board. The agent was able to confirm that my situation (similar to the OP's with partial residency in multiple states) was being handled correctly and that I wasn't missing anything. The peace of mind was worth it, and I saved myself what would have been probably another day of redial attempts and hold music. Still not sure how they do it but it definitely works!

From personal experience, you're fine not having a full-year residency in any state. I did this for 2 years while working seasonal jobs (ski resort in winter, fishing boat in summer, traveling in between). Just document your timeline clearly! I got flagged for audit once and had to prove my residency patterns. Having a calendar with dates and locations saved me big time. Also, depending on how long you've been abroad, look into the Foreign Earned Income Exclusion which might apply to some of your income if you meet certain requirements.

Quick question about e-filing in this situation - has anyone successfully e-filed with no full-year state residency? When I tried last year, TurboTax kept giving me errors and forcing me to choose a "home state" even though I didn't have one.

This is actually a pretty common situation for people with mobile lifestyles! You're correct that you can be a non-resident or part-year resident in all states you lived in without being a full-year resident anywhere. One thing to double-check though - make sure you understand Colorado's rules about "domicile" vs "residency." Even if you weren't there 183+ days, if Colorado considers itself your domicile (basically your permanent home base where you intend to return), they might still try to claim you as a full-year resident for tax purposes. Since your mail goes to your friend's place there and you're returning there, you might want to clarify this with Colorado's tax department. Also, since you've been in South America since September, depending on how your income was structured and how long you stay abroad, you might qualify for some foreign income exclusions on your federal return. Worth looking into if you're doing any work while traveling. Keep all your documentation (lease agreements, employment contracts, travel records) - the IRS and state agencies love clear timelines when dealing with multi-state situations like yours.