In ERCOT, a large customer's transmission bill for a whole year can depend on what it was doing in four 15-minute windows the summer before. That mechanism is 4CP, short for four coincident peak. It is why Texas factories, crypto miners and data centers watch the grid on hot afternoons in June through September. This post explains the rule from the Texas Administrative Code, who pays on it, when the recent peaks actually fell, and the 2026 proposal to replace it. Every figure links to the PUCT, ERCOT or a utility tariff.
Key takeaways
- 4CP is the average of ERCOT's system peak demand in June, July, August and September, each measured in a 15-minute settlement interval (16 TAC §25.192; ERCOT Nodal Protocols §9.17.1).
- ERCOT's average 4CP was 81,042.7 MW in 2024 and 80,859.8 MW in 2025 (ERCOT 4CP report NP9-83-M).
- On Oncor's system, a premises that has hit 700 kW in any previous billing month is billed transmission on its 4CP kW (Oncor retail delivery tariff, Rider TCRF).
- Texas SB 6 (2025) ordered the PUCT to review 4CP. In July 2026 the Commission approved a proposed rule to replace it with a 12CP, 30-minute method; it is not final (PUCT Project 58000).
What 4CP ERCOT actually measures
1. The peaks. For each summer month, ERCOT takes the highest 15-minute MW peak on the whole ERCOT transmission grid (Nodal Protocols §9.17.1(3)).
2. The wholesale rate. Under 16 TAC §25.192, each transmission service provider's wholesale rate is its commission-approved transmission cost of service divided by the average ERCOT coincident peak demand for June through September (§25.192(b)(1)).
3. The distribution provider's share. Each distribution service provider (DSP) is billed monthly on its previous year's average demand during those four intervals — the four intervals coincident with the ERCOT system peak, "divided by four". ERCOT files these figures by December 1 for use in the next year's billing, and wholesale storage load is excluded (same rule, §25.192(d)).
ERCOT describes the output as "DSP level average 4-CP load ratio shares which are used by the PUCT in the allocation of Transmission Cost of Service for the ERCOT Region" (ERCOT market notice).
Who pays on 4CP
Wholesale charges land on distribution utilities, and the utilities pass them to retail customers through their tariffs. On Oncor's system, "Any Premises that has established an NCP kW of at least 700 kW in any previous billing month" is billed on 4CP kW. Oncor measures 4CP kW as the customer's average 15-minute demand at the four monthly ERCOT system peaks of the previous calendar year, reset each January 1 (Oncor tariff, Rider TCRF). Other utilities' tariffs set their own terms, so check your utility's schedule.
The consequence: a customer that cuts load during all four peak intervals lowers its transmission charge for the following year. A customer that runs flat out in one of them pays for it all year. That is the incentive behind "4CP season" load curtailment.
When the 4CP peaks fell in 2024 and 2025
From ERCOT's annual 4CP calculation files, 4CP20241125.xlsx and 4CP20251124.xlsx, in report NP9-83-M (the "Total" row). ERCOT's list keeps only the most recent annual files, so older years drop off over time:
| Month | 2024 interval | 2024 MW | 2025 interval | 2025 MW |
|---|---|---|---|---|
| June | Jun 30, 17:45 | 79,749.8 | Jun 19, 17:00 | 77,485.8 |
| July | Jul 1, 17:00 | 81,184.4 | Jul 30, 17:00 | 81,908.3 |
| August | Aug 20, 17:00 | 85,357.6 | Aug 18, 17:00 | 83,968.5 |
| September | Sep 20, 16:00 | 77,878.8 | Sep 4, 17:30 | 80,076.5 |
| Average | 81,042.7 | 80,859.8 |
Times are as listed in ERCOT's files. The files label only date and time, so check ERCOT's report documentation for the interval convention before building a model on them. The figures exclude wholesale storage load and DC tie exports. ERCOT had not published the 2026 4CP intervals when this was written; it files each year's figures by December 1.
Two patterns stand out:
- Every interval fell in the late afternoon.
- The June 2024 and September 2025 peaks came near the edges of the season, not at its midsummer height. That is why 4CP is hard to predict — see how a grid forecast is built.
4CP is under review: SB 6 and the 12CP proposal
- SB 6 (signed June 20, 2025, effective immediately) directed the PUCT to evaluate "whether the current four coincident peak methodology… ensures that all loads appropriately contribute". It named alternatives such as multiple seasonal peaks, and required rule amendments by December 31, 2026 (SB 6 enrolled text; bill history).
- PUCT staff report, May 4, 2026 (Project 58484) recommended "replacing the 4CP methodology, measured on a 15-minute interval, with a 12CP methodology, measured on a 30-minute interval" (staff memo and draft report, ZIP containing a PDF).
- Proposed rule, Project 58000. The Commission approved the proposal for publication at its July 9, 2026 open meeting (PUCT filing). It would use 12 monthly 30-minute peak intervals running October through September (proposal). Comments were due August 11, 2026.
As of this writing we found no adopted rule and no confirmed start date for 12CP billing. Until the PUCT adopts one, 4CP is still the rule in §25.192.
Watching for a 4CP interval
No public source tells you in advance which interval will be the monthly peak. Customers watch ERCOT's load forecast and real-time demand on hot afternoons. The ZoningLabs ERCOT live grid status page summarises current Texas grid load, the forecast peak and prices from ERCOT's public data, with an as-of timestamp. ERCOT's own dashboards remain the authoritative source, and the data is the same public data other services use.
FAQ
What does 4CP mean in ERCOT?
4CP means four coincident peak: the ERCOT system's highest 15-minute demand in each of June, July, August and September. The average of those four readings allocates transmission cost of service among distribution providers, and many large customers are billed on their own demand during those intervals.
Who is billed on 4CP ERCOT charges?
Wholesale 4CP charges go to distribution service providers. At retail, utility tariffs set who is billed on 4CP kW. On Oncor's system, a premises that has reached at least 700 kW in any previous billing month is billed transmission on its 4CP kW.
When is 4CP season?
June 1 through September 30. Each month contributes one 15-minute interval: the ERCOT system peak for that month.
When were the 2025 4CP intervals?
According to ERCOT's 4CP report, June 19, July 30, August 18 and September 4, 2025, with an average 4CP of 80,859.8 MW.
Is ERCOT replacing 4CP with 12CP?
Proposed, not decided. After SB 6, PUCT staff recommended 12 monthly 30-minute peaks. The Commission approved a proposed rule for comment in July 2026, but a final rule had not been adopted when this was written.
Can I avoid 4CP charges?
A customer billed on 4CP lowers next year's transmission charge by reducing load during the four peak intervals. Because the intervals are only known after the fact, that means curtailing on the likely peak afternoons, at a real cost to operations.
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