Demand Overview

Market Demand

Market Demand (referred to as total energy in the 'Totals' reports below) represents the total energy that was supplied from the IESO-administered market. The IESO calculates total market demand by summing all output from generators registered in the market plus all scheduled imports to the province. It is also equal to the sum of all load supplied from the market plus exports from the province, plus all line losses incurred on the IESO-controlled grid.

Real-time demand on IESO reports site

The Realtime Constrained Totals Report provides Ontario demand, total energy (market demand), and scheduled operating reserve established by the IESO for each 5-minute interval of the current hour.

The Predispatch Constrained Totals Report provides a forecast of total energy (market demand), and operating reserve requirements for the current day. At 15:00 EST, a report is published looking out 24 hours.

The IESO forecasts demand to ensure that sufficient generation will be available to meet the peak for the current interval, hour, day, next day and weeks ahead. The Adequacy Report publishes information on Ontario’s electricity requirements for today through 34 days out.

For historical Ontario and market demand numbers, see Data Directory (Demand - Realtime Constrained Totals Report)

Ontario Demand

Ontario demand represents the total energy that was supplied from the IESO-administered market for the sake of supplying load within Ontario. It is also equal to the sum of all loads within Ontario which is supplied from the market, plus all line losses incurred on the IESO-controlled grid.

18-month demand forecast

The IESO forecasts demand for electricity in the province for the next 18-months and assesses whether the existing and proposed generation and transmission facilities are adequate to meet those needs. Normal weather forecasts represent a typical peak for that time of year, while extreme weather peaks reflect severe weather conditions, such as humidex of 50°C.

Source: Reliability Outlook, released March 24, 2025 updated quarterly.

Planned: Forecasted Seasonal Peaks

Planned: Historical and Forecast Energy Summary