You will file as a part year resident in CO the last 4 months of the year. It appears your military home of record (resident state) was FL until retirement and the subsequent change to CO.
FL does not have a state income tax so you don't have to file there.
For the eight months stationed in CO, as a FL resident: According to the CO Department of Revenue, a nonresident service member is not required to report his/her military income to Colorado. However, if the service member earned nonmilitary Colorado income, this income must be reported to Colorado for income tax purposes. The service member must pay Colorado tax on the following: nonmilitary Colorado salaries, nonmilitary Colorado wages, nonmilitary Colorado tips, nonmilitary Colorado commissions, income from a Colorado business, income from rents, royalties and/or gains from the sale of tangible personal property or real property located in Colorado.
So what remains is the military retirement pay for the remaining 4 months. In Colorado for tax year 2020 up to $24,000 of military retirement pay is exempt for retirees age 65 and older; $20,000, for those ages 55 to 64; and $7,500, for military retirees under age 55 (increasing to $10,000 in 2021 and $15,000 in 2022 and 2023).
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