Qualified dividends are taxed at the preferential long-term-capital-gain rates instead of ordinary rates, but only if the issuer qualifies and the holder meets the period test. For most common stock the test is more than 60 days during the 121-day period beginning 60 days before the ex-dividend date; preferred stock dividends attributable to long periods use 90 days in a 181-day window.
Days on which risk of loss was diminished do not count. Writing a deep in-the-money covered call, holding a matching short position, or buying a put can therefore disqualify an otherwise fine dividend.
Your broker applies the test and reports the qualified portion on form-1099-b and the dividend statement, but the calculation depends on data your broker may not have if you hedged elsewhere.
General information for the United States, not tax advice. Rules change and depend on your circumstances; confirm with a professional.
Related: long-term-capital-gain, dividend, holding-period, covered-call, straddle-rules