Two student flats can use the same number of kilowatt-hours and still face different electricity charges. Under a time-of-use arrangement, the usage total does not contain all the information needed: when that energy was consumed also matters. A low headline off-peak rate is therefore insufficient for estimating the bill.

The Ontario Energy Board explains time-of-use periods and the relationship between a bill and kilowatt-hours. Its Ontario-specific schedule is not a timetable for another country or utility. This article uses the underlying pricing distinction for an independent fictional calculation. No price or consumption figure below is an actual tariff, student average or recommended level of energy use.

Calculate energy charges by period

Suppose a fictional plan charges 0.30 units per kWh during a peak period and 0.12 during an off-peak period. Assume a fixed monthly charge of 10, with no other charges or taxes in this simplified example. Total monthly use is 100 kWh.

Usage allocation Peak charge Off-peak charge Total including fixed 10
60 peak, 40 off-peak 60 × 0.30 = 18 40 × 0.12 = 4.80 32.80
30 peak, 70 off-peak 30 × 0.30 = 9 70 × 0.12 = 8.40 27.40
0 peak, 100 off-peak 0 100 × 0.12 = 12 22

Moving 30 kWh from the first period to the second reduces the illustrative bill by 30 × (0.30 − 0.12) = 5.40. Total consumption remains 100. The final row is a mathematical boundary, not a claim that a household can safely or practically move all consumption overnight.

Compare with a flat rate on equal terms

Imagine an alternative fictional flat rate of 0.20 per kWh with the same fixed charge of 10. Its 100 kWh bill is 30. The first time-of-use allocation is 2.80 more expensive, while the second is 2.60 cheaper. Choosing a plan from its cheapest advertised period would miss that reversal.

Let p be peak kWh out of the same total 100. The time-of-use energy charge is 0.30p + 0.12(100 − p), or 12 + 0.18p. Matching the flat energy charge of 20 requires p = 8 / 0.18, approximately 44.44 kWh. This threshold applies only to these invented prices, equal fixed charges and exactly two periods.

A real comparison may have additional periods, seasonal changes, different standing charges, taxes, discounts or minimum charges. Account for those separately. Do not insert a third period into the off-peak column simply because its name sounds similar.

Distinguish controllable from necessary use

Separate energy tied to unavoidable needs from loads that can reasonably move. Heating, cooling, accessibility equipment and food storage cannot be treated like an optional charging session. Follow equipment instructions, accommodation rules and relevant safety guidance. A potential tariff saving does not establish that unattended operation or a change in essential use is appropriate.

In shared housing, identify the account holder, meter coverage and allocation method. A student charged a fixed included-utilities amount may receive none of the marginal saving shown here. Conversely, a shared bill needs an agreed method that does not invent each person's consumption from room size alone.

Before choosing a real plan, obtain the current tariff and a suitable usage breakdown from the actual supplier or meter records. Record the dates covered and whether the data represent a winter month, summer month or full year. The useful decision is a bill comparison under feasible schedules, with uncertain components visible, rather than a promise based on the cheapest hour in an advertisement.