1099 Contractor in Colorado with a Connecticut Client: Where Do You File?
Answer
Two possible returns, one certainty. The certainty is Colorado, which taxes residents on all self-employment income and expects quarterly estimated payments. The possibility is Connecticut, which taxes nonresidents on services actually performed inside the state — invoices sent there do not count.
Last verified
The client's location is the wrong thing to track. What matters is where you were sitting when you did the work — which is why a contractor's exposure to Connecticut is measured in days on the ground rather than in invoices sent.
Connecticut publishes no de minimis day count or dollar floor for nonresidents. Any Connecticut-source wage income above the state's general filing threshold requires a nonresident return, and that threshold is reset each year — check the current figure on the Connecticut Department of Revenue Services nonresident instructions before filing.
What you file
- 1Quarterly estimated payments · Colorado
Make quarterly estimated payments to Colorado Department of Revenue — Taxation Division on your full self-employment income — nothing is withheld from a 1099.
- 2Nonresident return · ConnecticutForm CT-1040NR/PY
File a Connecticut nonresident return only if you performed services inside Connecticut. Connecticut publishes no de minimis day count or dollar floor for nonresidents. Any Connecticut-source wage income above the state's general filing threshold requires a nonresident return, and that threshold is reset each year — check the current figure on the Connecticut Department of Revenue Services nonresident instructions before filing.
- 3Resident return · ColoradoForm DR 0104CR
File the Colorado resident return last and claim the credit for any tax paid to Connecticut.
The two states, side by side
| Colorado | Connecticut | |
|---|---|---|
| Taxes wages | Yes — flat | Yes — graduated |
| Reciprocity partners | None | None |
| Convenience rule | No | Only against convenience-rule states |
| Nonresident return | Form DR 0104 with Schedule DR 0104PN | Form CT-1040NR/PY |
| Credit for other-state tax | Form DR 0104CR | Schedule 2 (Form CT-1040) |
| Nonresident safe harbour | None published | None published |
| Local income tax | Yes | No |
| Revenue department | Colorado Department of Revenue — Taxation Division | Connecticut Department of Revenue Services |
| Last verified |
The other direction
Reversing the commute does not always reverse the answer. Living in Connecticut and working in Colorado gives:Home state, plus the client state if you work there.
Same two states, different situation
The withholding answer turns on how you are paid and where the work happens, not only on which two states are involved.
- W-2 commuter: Colorado → ConnecticutBoth states — credit offsets the double tax
- Remote worker: Colorado → ConnecticutHome state only
- Moved mid-year: Colorado → ConnecticutTwo part-year returns
Other Colorado pairs
Questions people actually ask
I live in Colorado and my client is in Connecticut. Do I have to file a Connecticut tax return?
Two possible returns, one certainty. The certainty is Colorado, which taxes residents on all self-employment income and expects quarterly estimated payments. The possibility is Connecticut, which taxes nonresidents on services actually performed inside the state — invoices sent there do not count.
Do reciprocity agreements help a 1099 contractor?
No. Every state reciprocity agreement in the country is an arrangement about wage withholding between two revenue departments, and a 1099 has no withholding to switch off. Whether Colorado and Connecticut hold an agreement makes no difference to a self-employed filer — sourcing rules decide the answer instead.
How current is this?
The Colorado and Connecticut rules on this page were last checked against Colorado Department of Revenue — Taxation Division and Connecticut Department of Revenue Services on 2026-08-07. We re-check the full grid every December after state legislative sessions close, and re-check the convenience-of-the-employer states quarterly because that is where the rules move fastest.
Sources
Every fact above comes from the revenue department that publishes the rule. We do not cite secondary summaries, and we do not restate a figure we could not find at source.
- Colorado Department of Revenue — Taxation Division — individual income taxaccessed 2026-08-07
- Connecticut Department of Revenue Services — individual income taxaccessed 2026-08-07