The Final Countdown, Revisited: DTCC's T+1 Testing and Conversion Weekend
Updated October 2026, after T+1 took effect. First published March 2024.
In March 2024 this post previewed DTCC's plan for the Memorial Day weekend switch to T+1. The weekend is long past. This update looks back at how the readiness program ran, from the first white paper to the conversion weekend. It draws on what DTCC and the industry groups published before and after go-live on May 28, 2024.
The Program, From White Paper to Go-Live
The industry's T+1 After Action Report, published by SIFMA, ICI, and DTCC in September 2024, lays out the sequence:
- February 2021: DTCC publishes a white paper, "Advancing Together: Leading the Industry to Accelerated Settlement."
- April 28, 2021: SIFMA, ICI, and DTCC announce they'll lead the effort together.
- December 2021: the three publish "Accelerating the U.S. Securities Settlement Cycle to T+1." An industry steering committee and working groups form, and over the next 24 months their sessions draw more than 100 participants.
- August 2022: the T+1 Industry Implementation Playbook comes out, with timelines and suggested work across trade processing, asset servicing, documentation, securities lending, prime brokerage, and funding and liquidity.
- February 15, 2023: the SEC adopts the rules and sets May 28, 2024 as the compliance date.
- August 2023: the T+1 Industry Command Center is set up, and industry testing opens on August 14.
- March 2024: DTCC publishes its T+1 Conversion Guide for the weekend.
How the Testing Worked
DTCC ran 21 two-week test cycles from August 14, 2023 through May 31, 2024. The test covered DTCC's ITP, NSCC, and DTC, plus Cboe, Nasdaq, and OCC. No regulator or industry group required firms to take part. DTCC called testing "highly recommended" and let firms join as many cycles as they wanted.
The scenarios went past normal trading days. Firms could test holiday processing, corporate actions such as stock splits and tender offers, double-settlement days, and recovery from deliberate system breaks. Michele Hillery, DTCC's general manager of equity clearing and DTC settlement service, put it plainly: "The message should be loud and clear for everyone: test and be ready."
Participation in the first week was uneven. All of NSCC's 30 largest clients had connected and started testing. At ITP, 90% of the 10 largest clients and 55% of the 30 largest had started. At DTC, the numbers were 70% of the top 10 and 15% of the top 30.
The Warning Two Months Out
Testing exercised the systems. The affirmation numbers measured something else: whether the people and processes behind each trade could finish on trade date. In March 2024, DTCC reported that 73% of transactions were affirmed by its 9:00 p.m. ET trade-date cutoff in January and 74.5% in February, and it recommended that firms affirm more than 90% of their transactions by that cutoff.
The February breakdown showed where the gap was. Prime brokers were at 83%. Investment managers using central matching were at 89%, down from 92% in January. Custodians and managers affirming their own trades were at 53%.
The Conversion Weekend
DTCC's plan, as John Abel, its executive director of clearance and settlement product management, described it in the conversion guide announcement, was meant to be "transparent to clients as we 'flip the switch' from T+2 to T+1." Production ran on T+2 through close of business on Friday, May 24. Monday was Memorial Day. Activity submitted on Tuesday, May 28 ran in a fully converted T+1 environment.
That put two days of trades into settlement on Wednesday, May 29: Friday's trades on T+2 and Tuesday's on T+1. The industry called it the "double-settlement" day, and it was one of the scenarios firms could rehearse in testing. SIFMA hosted the Command Center from May 24 to May 31 with ICI and DTCC, and kept a bridge line open for more than 48 hours from May 28 to May 30 while the industry worked through it. Separate calls kept regulators briefed. What happened on May 29 covers the fail rates and affirmation figures for that week.
What DTCC Reported After
By July 31, 2024, the industry was affirming nearly 95% of transactions by the 9:00 p.m. cutoff. The segment figures in the after-action report show how far each group moved since January:
| Segment | January 2024 | July 31, 2024 |
|---|---|---|
| Prime brokers | 81% | 98% |
| Investment managers, central matching | 92% | 96% |
| Custodians or managers, self-affirmation | 51% | 88% |
Self-affirmation improved the most and still finished last. The report doesn't say how that group closed the gap, whether through later hours, a move to central matching, or something else.
The same report put the average NSCC Clearing Fund under T+1 at $9.8 billion, down $3.0 billion from the three-month T+2 average. The Case for T+1 looks at what that number does and doesn't prove.
What to Copy for the Next Migration
Europe is next, with its move to T+1 planned for October 2027 according to DTCC. Two parts of the U.S. program are worth copying.
First, the test plan rehearsed the odd days, including the holiday and the double-settlement day, and it included scenarios that simulated system breaks. Second, DTCC published affirmation rates by segment months before go-live. Those numbers were unflattering, and they told firms where to spend the last two months.
If your firm trades in Europe, one lesson from the U.S. data applies directly: your affirmation rate depends on your slowest counterparty. Ask your custodians and managers how they affirm before the cutover, and track the answer by counterparty once you're live.
This post is for informational purposes only and does not constitute legal advice. For guidance on specific regulatory obligations, consult your counsel or compliance advisor.