Even one day counts. While you can always contribute to an IRA, you can't always deduct the entire amount. There are income limitations.
Is my IRA contribution deductible on my tax return?
If neither you nor your spouse is covered by a retirement plan at work, your deduction is allowed in full.
For contributions to a traditional IRA, the amount you can deduct may be limited if you or your spouse is covered by a retirement plan at work and your income exceeds certain levels.
Roth IRA contributions aren't deductible.
https://www.irs.gov/retirement-plans/retirement-plans-faqs-regarding-iras
