# Citi trading algorithm sells $1.4bn of European stocks after an input error; UK and German fines

Source: https://www.bankingnewsai.com/ai-incidents/citigroup-2022-flash-crash-trading-algorithm
Last updated: Oct 21, 2026

Citigroup (Citigroup Global Markets Limited) · Institution's own AI · severity 4 of 5

On 2 May 2022 a Citigroup Global Markets Limited (CGML) trader in London meant to sell a US$58m equity basket but entered a US$444bn one. Per the FCA, controls blocked US$255bn, but the remaining US$189bn went to an automated VWAP trading algorithm that sold US$1.4bn of shares across European exchanges before the order was cancelled, coinciding with a brief fall in several indices and a US$48m loss for CGML. In May 2024 the FCA (£27.8m) and PRA (£33.9m) fined CGML a combined £61.6m for missing hard blocks, a click-through alert and slow monitoring; BaFin fined Citi's German unit €12.975m. Citi called it an individual error corrected within minutes. The execution algorithm was not described as AI.

## Key facts

|  |  |
| --- | --- |
| Date | May 2, 2022 |
| Institution | Citigroup (Citigroup Global Markets Limited) |
| Country | United Kingdom |
| AI system | CitiSmart (VWAP execution algorithm) fed by the PTE order management system · Automated algorithmic order-execution system; not described as AI · vendor: Citigroup (in-house) |
| AI? | Automated system not described as AI — The system was automated, but neither the institution nor a regulator described it as AI; it is listed because it is routinely discussed as an AI failure. |
| Category | Trading automation (Institution's own AI) |
| Status | Regulator finding |
| Severity | 4 of 5 — Combined fines of £61.6m from the FCA and PRA plus €12.975m from BaFin, a US$48m trading loss and a brief drop in several European indices put this above the regulatory-finding level. |

## What happened?

On the morning of 2 May 2022, a UK bank holiday, a trader on CGML's Delta 1 desk loaded a basket of equities into the desk's order management system, PTE, entering the intended US$58m in the unit-quantity field instead of the notional-value field. Per the FCA's Final Notice, this created a basket with a notional size of US$444bn comprising 349 stocks across multiple European markets. A 'Trade Limit Warning' pop-up listed 711 warnings, of which only the first 18 lines were visible without scrolling; the trader overrode the soft warnings. [1][3]

Two hard blocks in PTE stopped US$248bn of the basket. The remaining orders were routed into CitiSmart, Citi's electronic algorithmic trading system, where controls blocked further orders before about US$189bn was sent for execution by a volume-weighted average price (VWAP) algorithm designed to sell over the rest of the day. US$1.4bn of sell orders were executed on exchanges in 13 countries before the trader cancelled the remaining orders at 09:10. The FCA said the MSCI Europe ex UK index fell just over 4% within five minutes of the basket starting to trade, and that the incident caused a US$48m loss for CGML. [1][2][7]

Citi said the same day that one of its traders had made an error when inputting a transaction and that it identified and corrected it within minutes. Sweden's OMX 30 index fell by as much as 8% before paring most of the loss, CNBC and The Guardian reported. [6][7]

The regulators found the failure lay in Citi's controls rather than the trader alone. The FCA said there was no hard block that would have rejected the whole erroneous basket (one existed on Citi's New York Delta 1 desk since 2013 but had not been rolled out to the EMEA desk), the pop-up could be clicked through, a key CitiSmart price control had been loosened from 5% to 15% in March 2020 and never reviewed, and real-time monitoring was too slow to escalate alerts. The PRA said CGML had received repeated supervisory communication on strengthening its trading controls between April 2018 and May 2022. BaFin said Citi's German subsidiary, which had outsourced its algorithmic-trading monitoring to CGML in London, remained responsible for a system that failed to detect the manual input error. [1][2][4][5]

## Timeline

- May 2, 2022 — A CGML trader's input error creates a US$444bn equity basket; an automated VWAP algorithm sells US$1.4bn of European shares before the order is cancelled at 09:10. Citi says the error was corrected within minutes. [1][6][7]
- May 13, 2022 — Citi adds a US$4bn basket-level hard block to PTE, having cut the per-order hard block from US$2bn to US$250m on 5 May and restored the CitiSmart price control to 5% on 6 May. [1]
- Jul 14, 2022 — The PRA imposes a section 166 skilled-person requirement on CGML, under which it carries out a remediation and validation exercise. [1]
- May 22, 2024 — The FCA fines CGML £27,766,200 and the PRA fines it £33,880,000, a combined £61.6m, after 30% settlement discounts. [2][4][8]
- May 24, 2024 — BaFin fines Citigroup Global Markets Europe AG €12,975,000 for lacking appropriate trading thresholds and limits; the fine is published on 20 June 2024. [5][9]

## What was the impact?

- Financial: US$1.4bn of erroneous sell orders executed; US$48m trading loss for CGML; fines of £61.6m (FCA and PRA) and €12.975m (BaFin)
- Customers: No customer losses reported; the orders were Citi's own hedging trades
- Other: The FCA said the trades coincided with a material short-term drop in several European indices lasting a few minutes, with the MSCI Europe ex UK index down just over 4% within five minutes. [1][4][5]

## How did Citigroup (Citigroup Global Markets Limited) respond?

Citi said on 2 May 2022: "This morning one of our traders made an error when inputting a transaction. Within minutes, we identified the error and corrected it." After the UK fines it said: "We are pleased to resolve this matter from more than two years ago, which arose from an individual error that was identified and corrected within minutes. We immediately took steps to strengthen our systems and controls, and remain committed to ensuring full regulatory compliance." CGML did not dispute the FCA's findings and agreed to settle. [2][6][8][9]

## What was the outcome?

The FCA found breaches of Principles 2 and 3 and MAR 7A.3.2 and fined CGML £27,766,200 (£39,666,000 before the settlement discount); the PRA found breaches of Fundamental Rules 2, 5 and 6 and its algorithmic-trading rules and fined CGML £33,880,000 (£48,400,000 before discount). BaFin's €12,975,000 fine on Citigroup Global Markets Europe AG is final and binding. Citi added a basket-level hard block, tightened per-order limits and recalibrated CitiSmart controls within days, and completed a PRA-required skilled-person remediation exercise. [1][3][4][5]

## FAQ

### Was the Citi flash crash caused by AI?

No. The regulators describe a manual input error by a trader that passed through an order management system and was executed by an automated VWAP trading algorithm in Citi's CitiSmart platform. Neither the FCA, the PRA nor BaFin described the system as artificial intelligence; their findings concern missing hard blocks, a click-through alert and slow monitoring.

### How much was Citi fined for the May 2022 flash crash?

The FCA fined Citigroup Global Markets Limited £27,766,200 and the PRA fined it £33,880,000 in May 2024, a combined £61.6m after 30% settlement discounts. BaFin separately fined Citigroup Global Markets Europe AG €12,975,000 on 24 May 2024 for the same trading incident.

### Was any money lost in the Citi trading error?

The FCA said the trading incident resulted in a US$48m loss for CGML. About US$1.4bn of shares were sold across European exchanges before the order was cancelled, and several indices dropped briefly. No customer losses have been reported; the orders were Citi's own trades.

### What did Citi change after the flash crash?

Per the FCA's Final Notice, within days Citi cut its per-order hard block in PTE from US$2bn to US$250m, restored a CitiSmart price control from 15% to 5%, and added a US$4bn basket-level hard block and a 95% average-daily-volume hard block. It then carried out a remediation exercise under a PRA skilled-person requirement.

## Sources

1. [Final Notice: Citigroup Global Markets Limited](https://www.fca.org.uk/publication/final-notices/citigroup-global-markets-limited-2024.pdf) — Financial Conduct Authority, May 17, 2024 (official): "The trader had intended to sell a basket of equities to the value US$58m. However, the trader erroneously loaded a basket with a notional size of US$444bn comprising 349 stocks, across multiple European markets."
2. [FCA fines CGML £27,766,200 for failures in its trading systems and controls](https://www.fca.org.uk/news/press-releases/fca-fines-cgml-27-million) — Financial Conduct Authority, May 22, 2024 (official): "CGML controls blocked US$255bn of the basket progressing, but not the remaining US$189bn which was sent to a trading algorithm."
3. [Bank of England and PRA final notice - Citigroup Global Markets Limited](https://www.bankofengland.co.uk/-/media/boe/files/prudential-regulation/regulatory-action/final-notice-from-boe-and-pra-to-citigroup-global-markets-limited.pdf) — Bank of England (Prudential Regulation Authority), May 17, 2024 (official): "The immediate cause of the trading error was an input mistake by a trader, but as a result of primary control failings, erroneous orders with a notional size of US$196bn were generated in the Firm's electronic trading system, CitiSmart, for execution and were not subsequently cancelled in their entirety"
4. [The PRA fines Citigroup Global Markets Limited £33,880,000 for failures in its trading systems and controls](https://www.bankofengland.co.uk/news/2024/may/pra-fines-citygroup-global-markets-limited) — Bank of England (Prudential Regulation Authority), May 22, 2024 (official): "Throughout the relevant period, CGML received repeated supervisory communication from the PRA on the need to strengthen its trading controls."
5. [Citigroup Global Markets Europe AG: BaFin imposes administrative fine](https://www.bafin.de/SharedDocs/Veroeffentlichungen/EN/Massnahmen/40c_neu_124_WpHG/meldung_2024_06_20_CitigroupGlobalMarketsEuropeAG_en.html) — BaFin, Jun 20, 2024 (official): "This system failed to detect a manual input error made by one of the company's traders. The resulting erroneous orders caused a market disruption."
6. [Citigroup says trader made error behind 'flash crash' in Europe](https://www.theguardian.com/business/2022/may/03/citigroup-trader-error-flash-crash-markets-falls) — The Guardian, May 3, 2022 (news): ""This morning one of our traders made an error when inputting a transaction," the New York-based bank said in a statement on Monday night. "Within minutes, we identified the error and corrected it.""
7. [Citi says a trader error caused Europe's 'flash crash.' Here's how it unfolded](https://www.cnbc.com/2022/05/03/flash-crash-europes-stock-market-fall-triggered-by-citi-trader-error.html) — CNBC, May 3, 2022 (news): "Nordic stocks were hit the hardest, with Sweden's Stockholm OMX 30 share index falling by as much as 8% at one point, before paring most of those losses to close the session down 1.9%."
8. [Citigroup fined over 'fat finger' error that led to £1.1bn of mistaken orders](https://www.theguardian.com/business/article/2024/may/22/citigroup-fined-over-fat-finger-error-mistaken-orders) — The Guardian, May 22, 2024 (news): "We immediately took steps to strengthen our systems and controls, and remain committed to ensuring full regulatory compliance."
9. [Citi fined $13.9M by Germany's BaFin over 2022 flash crash error](https://www.bankingdive.com/news/citi-fined-14m-germany-bafin-2022-flash-crash-error/719544/) — Banking Dive, Jun 21, 2024 (news): ""We are pleased to resolve this matter from more than two years ago, which arose from an individual error that was identified and corrected within minutes," Citi said Friday in an emailed statement to Banking Dive."

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