Cum-Ex and Cum-Cum Dividend Trades

Many countries withhold tax on dividends and let the true owner reclaim it, or a portion of it, if they're eligible (for example, a foreign pension fund under a tax treaty). Cum-ex trading exploited a settlement-timing gap: shares were sold "cum-dividend" (with the right to the dividend still attached) but delivered "ex-dividend" (after the entitlement date), momentarily leaving two parties both able to produce paperwork claiming to be the legitimate dividend recipient. Both then filed for a tax refund on withholding that was only ever paid once, and tax authorities — across several European countries — paid out billions before the scheme was understood and shut down.

Cum-cum trading is a related but distinct maneuver: a shareholder who wouldn't qualify for a reduced withholding rate temporarily transfers shares to a party who does qualify, just around the dividend date, then transfers them back afterward — capturing the lower rate on a dividend that economically still belongs to the original, non-qualifying holder. It doesn't manufacture extra refunds the way cum-ex did, but it still improperly exploits a treaty benefit the true economic owner wasn't entitled to.

Both schemes have been prosecuted as tax fraud (cum-ex explicitly so) and prompted most affected jurisdictions to close the settlement and documentation loopholes that made duplicate or improper refund claims possible.