The Short Version
When a seller fails to deliver shares by the settlement deadline (a 'short delivery'), the exchange's clearing corporation runs a special auction to obtain the shortfall on the buyer's behalf. This happens in a separate 'auction market' — a distinct trading session where only participants who actually hold and can deliver the specific security may offer it, at a price typically capped within a band set relative to the stock's recent trading range (to prevent auction sellers exploiting a defaulter's desperation). If no one offers enough shares in the auction to cover the shortfall, the transaction is instead 'closed out' — the buyer receives a cash payment instead of shares, usually calculated at the higher of the security's highest price over a specified recent period or a fixed premium over its closing price, so the buyer isn't left worse off for the seller's failure.
Explain It Like I'm 10
Imagine you pre-ordered a specific toy from a friend who promised to bring it to school by Friday, but Friday comes and they don't have it. The teacher steps in and asks around the whole school: 'does anyone actually have this exact toy they'd sell right now?' If someone does, the teacher buys it from them and hands it to you, then bills your friend for the cost (plus a penalty for being late). If literally nobody in the school has that toy to sell, the teacher instead just gives you cash — deliberately a generous amount — so you're not left empty-handed just because your friend didn't come through.
Step-by-Step Example
- 1 A seller fails to deliver 100 shares by the settlement deadline.
- 2 The clearing corporation runs an auction, where only investors who genuinely hold that stock can offer to sell it to fill the shortfall.
- 3 An auction seller offers 100 shares within the permitted price band; the clearing corporation buys them and delivers them to the original buyer.
- 4 The defaulting original seller is billed the auction price difference plus a penalty — the buyer isn't affected financially by the delay.
- 5 If no auction seller had come forward at all, the trade would instead be closed out in cash, at a price deliberately set high (e.g., the higher of the recent high or a premium over the closing price) so the original buyer is compensated fairly for not receiving the actual shares.
Quick Recap
- ✓ Auction sellers must actually hold the shares being offered — it's a genuine delivery, not another short sale.
- ✓ The defaulting original seller bears the full cost difference plus a penalty, regardless of the auction outcome.
- ✓ Close-out (cash settlement in lieu of shares) only happens when the auction itself fails to find enough sellers.
- ✓ Close-out pricing is deliberately set high (relative to recent prices) precisely so that failing to deliver is never cheaper than the auction/close-out cost — discouraging deliberate short deliveries.