When is it optimal to exercise an American call option early due to dividends, and how do you decide?

Early exercise of an American call option is potentially optimal only just before an ex-dividend date. The decision hinges on whether the dividend captured exceeds the time value sacrificed by exercising.\n\nThe Core Intuition:\n\nWhen a stock goes ex-dividend, its price drops by approximately the dividend amount. A call holder does not receive dividends. So an in-the-money call holder faces a dilemma: exercise before the ex-date to capture the dividend, or hold and suffer the price drop.\n\nThe Decision Rule:\n\nExercise is optimal when:\n\nDividend > C(S, K, T-t) - max(0, S - K)\n\nIn simpler terms: exercise if the dividend exceeds the remaining time value of the call.\n\nEquivalently, exercise if:\n\nDividend > K x [1 - e^{-r(T-t)}] + Put Value\n\nwhere the right side represents the time value components (interest savings from deferring the strike payment plus the embedded put value).\n\nWorked Example:\n\nHargrove Pharmaceuticals trades at $85. You hold an American call with K = $70, expiring in 40 days. The stock goes ex-dividend tomorrow with D = $3.00. Risk-free rate is 5%.\n\nTime value components:\n- Interest savings: $70 x [1 - e^{-0.05 x 40/365}] = $70 x 0.00548 = $0.38\n- Estimated put value (deep OTM 70 put with 40 days): approximately $0.05\n- Total time value if exercised: $0.38 + $0.05 = $0.43\n\nSince D = $3.00 > $0.43, exercise is optimal.\n\nBy exercising, you:\n- Pay $70 for a stock worth $85 (intrinsic value = $15)\n- Collect the $3.00 dividend\n- Sacrifice only $0.43 in time value\n- Net benefit of early exercise: $3.00 - $0.43 = $2.57\n\nIf instead D = $0.25, then $0.25 < $0.43, and you should not exercise early because the time value exceeds the dividend.\n\nKey Nuances:\n\n1. Only the last ex-dividend date before expiry matters for single-dividend stocks; for multiple dividends, check each ex-date sequentially from the last working backward\n2. Deep ITM calls with very low time value are more likely candidates for early exercise\n3. ATM or OTM calls should virtually never be exercised early because their time value is substantial\n4. European calls cannot be exercised early, so they trade at a discount to identical Americans when dividends are large\n\nDeepen your understanding with our CFA Derivatives question bank.