Day-ahead vs. real-time
Every morning the day-ahead market prices tomorrow, hour by hour. This page grades that bet against what the grid actually paid.
Two prices for every hour
Aug 18 · ET · 8-zone average- - day-ahead — real-timeWhere the misses landed
by zone and hour · click a zone to re-scope the chart aboveZone rows rank by today's average miss. zone mean of the load-zone settlement point prices.
The premium by hour
average spread by hourAverage of 718 paired hours since 2026-07-19. Fills in as the record grows.
The late-afternoon hours that decide the capacity tag are the hours day-ahead prices hardest. When this chart bulges violet after 2 PM, that is why.
Tomorrow is already priced
the day-ahead betAug 19, as the day-ahead market cleared it. Real time starts grading at midnight.
Today by zone
day-ahead vs real-time averages| Zone | Day-ahead avg | Real-time avg | Spread |
|---|---|---|---|
| Connecticut | $53.12 | $44.66 | −$6.65 |
| Maine | $51.79 | $43.40 | −$6.57 |
| NE Mass · Boston | $54.70 | $45.73 | −$7.17 |
| New Hampshire | $54.13 | $45.28 | −$6.98 |
| Rhode Island | $53.98 | $45.04 | −$7.13 |
| SE Massachusetts | $54.84 | $45.80 | −$7.30 |
| Vermont | $55.02 | $45.82 | −$7.19 |
| West/Central Mass | $54.33 | $45.48 | −$7.04 |
Real-time averages cover graded hours only. Full interval detail is on the prices page.
What is the day-ahead market?
ISO-NE clears a day-ahead market every morning: offers close mid-morning and results post in the early afternoon ET, locking an hourly price for every hour of tomorrow. Most New England load settles against those prices, and the real-time market trues up the difference every five minutes.
What is DART?
Trader shorthand for the day-ahead to real-time spread. On this page the spread is real time minus day-ahead, so a positive number means the hour settled above its day-ahead price and a negative number means day-ahead carried a premium.
Why do the two prices differ?
The day-ahead price embeds a forecast of weather, demand, and which plants will run. Real time is the grid as found. New England adds fuel exposure: the region leans on natural gas and imports, so a cold snap or a pipeline constraint shows up in real time first.
Where does this data come from?
ISO-NE's public data feeds: day-ahead hourly and real-time five-minute zonal prices for the eight load zones, the same feeds behind the prices page. On daylight-saving switch days the grid honestly shows 23 or 25 hours.