What actually happens
An employee who lives in Wyoming and performs work in Colorado sits in two tax systems at once. The residence state claims the right to tax all of a resident's income wherever earned; the work state claims the right to tax income sourced within its borders. Absent an agreement, both claims stand, and the conflict is resolved after the fact through a credit on the resident return rather than up front in payroll.
When Colorado withholding starts
Colorado requires withholding from the first dollar of in-state compensation. There is no de minimis day count to shelter a short assignment. Withholding required from the first dollar of wages for services performed in Colorado; no de minimis day or dollar safe harbor.
The trap is that thresholds are usually retroactive to the first day once crossed. An employee who spends 40 days in a 30-day-threshold state does not owe tax on 10 days; they owe it on all 40, and the employer is the one who failed to withhold.
Unemployment insurance goes to one state only
Income tax can be split between states. Unemployment insurance cannot. Under the localization test used by every state, an employee whose services are performed entirely in Colorado is covered by Colorado for unemployment purposes, and all wages are reported there — regardless of where they live, where you are headquartered, or which state's income tax you withhold. Colorado's 2026 taxable wage base is $30,600. The four-factor test in order.
Local taxes are a separate problem
Colorado: Several Colorado cities (Denver, Aurora, Glendale, Greenwood Village, Sheridan) impose an Occupational Privilege Tax -- a flat monthly per-employee 'head tax' with both an employee-withheld portion and an employer portion. It is not an income-based tax. Colorado also has the state-run FAMLI paid leave premium.
What you have to register for
| Obligation | State | Agency |
|---|---|---|
| Income tax withholding | Colorado | Colorado Department of Revenue |
| Unemployment insurance | Colorado | Colorado Department of Labor and Employment (CDLE) |
| Paid family & medical leave | Colorado | Colorado FAMLI 2026 premium is 0.88% of wages up to the Social Security wage base ($184,500), split 50/50: 0.44% employee, 0.44% employer. Employers with fewer than 10 employees owe no employer share but must still withhold the employee 0.44%. |
Frequently asked
Do Colorado and Wyoming have a reciprocal tax agreement?
No. There is no reciprocal agreement between Colorado and Wyoming. Colorado taxes wages earned in the state by nonresidents, and Wyoming does not tax wages at all.
Which state's income tax should be withheld?
Colorado, as the state where the work is performed. Wyoming imposes no wage income tax, so Colorado is the only withholding obligation.
Which state gets the unemployment insurance wages?
Colorado. Unemployment coverage is never split between states for a single job. The localization test assigns the whole job to the state where services are performed, which here is Colorado, regardless of residence or where the employer is headquartered.
How many days can an employee work in Colorado before withholding starts?
There is no safe harbour. Colorado requires nonresident withholding from the first dollar of compensation earned in the state, so even a single day of in-state work creates an obligation in principle.