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 26 · ET · 21-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 719 paired hours since 2026-07-27. Fills in as the record grows.
The late-afternoon hours that decide 5CP are the hours day-ahead prices hardest. When this chart bulges violet after 2 PM, that is the market paying in advance for the risk everyone curtails around.
Tomorrow is already priced
the day-ahead betAug 27, 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 |
|---|---|---|---|
| AECO | $31.80 | $21.93 | −$3.69 |
| AEP | $41.38 | $41.18 | +$11.50 |
| APS | $40.75 | $43.46 | +$14.68 |
| ATSI | $40.25 | $40.60 | +$10.91 |
| BGE | $46.79 | $50.38 | +$18.82 |
| COMED | $35.42 | $32.70 | +$9.60 |
| DAY | $43.56 | $46.82 | +$15.49 |
| DEOK | $43.30 | $59.07 | +$27.89 |
| DOM | $44.18 | $47.97 | +$17.48 |
| DPL | $32.01 | $20.06 | −$5.60 |
| DUQ | $38.41 | $40.34 | +$12.64 |
| EKPC | $42.08 | $43.51 | +$13.17 |
| JCPL | $32.59 | $24.80 | −$1.18 |
| METED | $34.66 | $32.41 | +$6.30 |
| OVEC | $41.45 | $45.96 | +$16.04 |
| PECO | $30.95 | $21.73 | −$3.49 |
| PENELEC | $39.11 | $37.00 | +$7.56 |
| PEPCO | $45.60 | $49.91 | +$18.85 |
| PPL | $31.12 | $27.96 | +$4.34 |
| PSEG | $32.90 | $25.25 | −$1.06 |
| RECO | $38.07 | $28.81 | −$1.65 |
Real-time averages cover graded hours only. Full interval detail is on the prices page.
What is the day-ahead market?
PJM clears a day-ahead market every morning: bids close late morning and results post in the early afternoon ET, locking an hourly price for every hour of tomorrow. Most PJM volume settles against those day-ahead prices, and the real-time market trues up the difference as the day actually unfolds.
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. In PJM an entire class of participants, virtual traders running INCs and DECs, exists to arbitrage exactly this number.
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. Each of the 21 transmission zones also carries its own congestion, which is why one zone's row can light up on the miss map while its neighbors stay quiet.
Is day-ahead usually higher?
Virtual bidding tends to keep the averages close, which is the point of allowing it. The tails are where it gets interesting: a heat wave or a fleet of outages can blow real time through the day-ahead price by hundreds of dollars, and overnight hours often settle under.
Where does this data come from?
PJM's public Data Miner 2: day-ahead hourly LMPs and real-time five-minute LMPs for the 21 transmission zones, the same feeds behind the prices page. The newest prices arrive unverified within minutes and are replaced when PJM's verified rows publish the next business day. On daylight-saving switch days the grid honestly shows 23 or 25 hours.