Thornton Business Filing Deadlines & Ongoing Requirements

Annual federal income tax return (extensions available via Form 7004 / 4868).

Free, one-time federal tax ID needed for tax filings, payroll and bank accounts.

Businesses holding property that has gone unclaimed — uncashed payroll or vendor checks, customer credits and refunds, unused gift cards, deposits — must report and turn it over to the state each year, after sending the owner a due diligence notice before the deadline. The annual report and payment are due November 1 for general property. Which state's law applies depends on the owner's last known address, or the business's state of incorporation when there is none, so a business can owe reports to several states.

A person or service with a physical Colorado address to receive legal notices and service of process; listed with Colorado Secretary of State.

Fee: $25. Required to keep the entity in good standing.

Corporate income tax.

If personal information of residents of the state is acquired without authorization, notify affected residents within 30 days of discovering the breach and the Attorney General if 500 or more residents are affected (Colo. Rev. Stat. 6-1-716). This is an event-driven duty, so it has no calendar date. Sources in the PR describe the state's rule in different words; check the statute for the exact trigger and content of the notice.

Colorado businesses return the personal property declaration schedule (DS 056) for taxable personal property owned on January 1 to the county assessor by April 15; the filing threshold is a total actual value per county (about $56,000 on recent forms; check the current form). A 10- or 20-day extension costs $20 or $40 if requested by April 15; a late filing penalty is the lesser of $50 or 15% of the tax. The county's own page was not individually confirmed; the state rule applies. The link is the state Division of Property Taxation page.

Home-rule cities (Denver, Aurora, Colorado Springs, etc.) self-collect sales tax and require their own licenses.

The commercial space must be approved for its intended use before operating.

All businesses in Thornton need a city sales and use tax business license, free of charge and with no annual renewal; a certificate of occupancy is also required for locations.

Withheld income tax, Social Security and Medicare, plus employer share, via EFTPS.

Quarterly reconciliation of wages and payroll taxes.

Annual FUTA return and payment.

Wage statements to employees and transmittal to the SSA.

Employment eligibility verification, retained for 3 years after hire or 1 year after termination.

Employers must post the FLSA minimum wage, FMLA (50+ employees), EEO, OSHA, USERRA and related notices in a conspicuous place.

Employer account for state unemployment insurance contributions.

Withhold state income tax from wages and remit on the assigned deposit schedule; file annual reconciliation and W-2s.

Quarterly wage report and contribution payment. Colorado taxes the first $30,600 of each employee's wages (2026); new employers pay 1.53%, and experience-rated rates range from 0.56% to 7.34%.

Federal law requires reporting each new hire within 20 days of hire (some states require sooner).

Required at: 1 employee.

Employers remit premiums quarterly via the FAMLI portal and may deduct up to half from employees.

Colorado requires employers with 1+ employees to provide paid sick leave, post notice and keep records.

State minimum wage, unemployment insurance, workers' compensation and anti-discrimination notices must be posted where employees can see them.

Employers in business at least two years with five or more employees and no qualified plan must register or certify an exemption. Penalty: $100 per eligible employee a year, up to $5,000, enforced one year after an employer's due date; pre-enforcement letters began August 15, 2025.

Employers with more than 10 employees keep Forms 300 and 301 for work-related injuries and illnesses, and post the Form 300A summary for the previous year at each establishment from February 1 through April 30. Records are kept five years. Report a work-related fatality within 8 hours and an inpatient hospitalization, amputation or loss of an eye within 24 hours.

Applicable large employers (50 or more full-time employees, counting part-time hours as full-time equivalents) give each full-time employee a Form 1095-C. The January 31 deadline is extended automatically by 30 days, to March 2 in most years (March 1 for the 2026 forms).

The transmittal Form 1094-C and each Form 1095-C are due to the IRS at the end of February on paper or March 31 electronically; employers filing 10 or more information returns in total must file electronically. Penalties apply per late or incorrect form.

Private employers with 100 or more employees file annually through the EEOC's online system; federal contractors with 50 or more employees and certain contracts have also filed. The EEOC sets each year's window (the 2024 report was due June 24, 2025, with no extensions), so check its data collections page.

Establishments with 250 or more employees submit their Form 300A summary through OSHA's Injury Tracking Application by March 2. Establishments with 20 to 249 employees in designated higher-hazard industries must also submit the summary, and those with 100 or more in the most hazardous industries submit Forms 300 and 301 data.

Quarterly estimated payments by owners on business income (Form 1040-ES), including self-employment tax.

Required for each non-employee paid $2,000 or more in the year (payments made after 2025).

Required before making taxable sales; register with the state tax agency.

Collect sales tax from customers and remit on the filing frequency assigned by the state.

Many Colorado cities and counties administer and collect their own sales and use taxes separately from the state; sellers register and file with each jurisdiction where required.

Home-based businesses need a home occupation permit and must comply with zoning limits (signage, customers, employees).

Colorado registers assumed names at the state level.