Direct answer
Multiply energy in each tariff period by that period's rate and add the charges. To test shifting, move the same kWh from one period to another and compare totals: simple energy-charge savings equal shifted kWh multiplied by the rate difference. Confirm the actual tariff calendar, seasonal rules, fixed and demand charges before treating the estimate as a bill saving.
What this calculation tells you
Electricity tariffs uses the relationship “charge = Σ(period kWh × period rate)”. The useful output is not merely a headline number: it keeps the inputs, units and calculation basis visible so the result can be checked and compared without changing the underlying question.
The two worked situations cover baseline month and shift 40 kwh off peak. Together with the “Same 350 kWh under different allocations” comparison, they show how the method behaves in materially different circumstances and where a real-world rule or measurement still has to come from outside the calculator.
Where it is used
baseline month
Off-peak use is 240 kWh at 0.16 and peak use is 110 kWh at 0.34. Energy charge is 75.80 for 350 kWh.
shift 40 kWh off peak
Total stays 350 kWh; off-peak becomes 280 kWh and peak becomes 70 kWh. Modeled saving is 7.20, equal to 40 × (0.34 − 0.16).
Same 350 kWh under different allocations
The table isolates timing because total energy and rates remain fixed.
When this guide helps
- You need to reproduce baseline month from explicit inputs rather than a rough estimate.
- You want to test shift 40 kwh off peak without carrying an assumption over silently from the first case.
- You need to reconcile the electricity tariffs result with “charge = Σ(period kWh × period rate)” before using it.
Calculate electricity tariffs with time-of-use energy charge
Copy time bands, rates and effective dates from the applicable tariff, then allocate measured or planned energy to those bands. Preserve total kWh when testing a pure schedule shift.
DOE explains that energy charges may vary by time and season and that other structures include demand, fixed and minimum charges. A valid comparison labels which components are and are not modeled.[1]
Validate the electricity tariffs result before using it
Add period kWh and compare with the source meter total. Divide each period charge by its kWh to reconstruct its rate, then confirm the shifted case preserves energy unless efficiency also changes.
Calculate savings independently as shifted kWh times the rate difference. It should match baseline charge minus shifted charge when only two energy rates are involved.
Mistakes that produce a convincing but wrong answer
Errors include placing boundary-hour usage in the wrong band, applying a weekend schedule on a weekday, ignoring seasonal rates, reducing total kWh during a supposed pure shift, and treating demand charges as kWh charges.
Do not shift a process where safety, comfort, noise, staffing or equipment instructions make the schedule unsuitable. The arithmetic does not approve operation.
What the calculation cannot decide
The calculator models entered peak/off-peak energy rates only. Taxes, fixed charges, demand charges, minimum bills, holidays and live utility rules are excluded unless represented elsewhere.
Verify the current tariff directly with the utility. DOE notes that rate selection should reflect the site's actual load and complete rate design.[1]
Worked case: baseline month
Off-peak use is 240 kWh at 0.16 and peak use is 110 kWh at 0.34.
Charge = 240 × 0.16 + 110 × 0.34 = 38.40 + 37.40 = 75.80.
Energy charge is 75.80 for 350 kWh.
This excludes any fixed, tax or demand component.[1]
Reproduce this worked caseOpen Time-of-Use Electricity Cost Calculator
Worked case: shift 40 kWh off peak
Total stays 350 kWh; off-peak becomes 280 kWh and peak becomes 70 kWh.
Charge = 44.80 + 23.80 = 68.60. Difference = 7.20.
Modeled saving is 7.20, equal to 40 × (0.34 − 0.16).
The saving exists only if the tariff and moved load match the entered scenario.[1]
Reproduce this worked caseOpen Time-of-Use Electricity Cost Calculator
Compare scenarios without changing the question
The “Same 350 kWh under different allocations” comparison changes a declared driver while retaining the time-of-use energy charge basis. Read the rows with the stated inputs and units so the difference can be attributed to the changed condition instead of to an unnoticed denominator or convention change.
The table isolates timing because total energy and rates remain fixed.
| Off-peak kWh | Peak kWh | Energy charge | Change |
|---|---|---|---|
| 240 | 110 | 75.80 | baseline |
| 280 | 70 | 68.60 | −7.20 |
| 310 | 40 | 63.20 | −12.60 |
Prepare a reliable input record for Time-of-Use Electricity Cost Calculator
Before opening the Time-of-Use Electricity Cost Calculator, create a compact input ledger. For every value, record its quantity, unit, period or reference date, where it came from, and whether it is measured, quoted, estimated or deliberately chosen. The governing relationship is “charge = Σ(period kWh × period rate)”, so each symbol and number must belong to that same basis. This preparation prevents a polished calculator output from concealing mixed units, duplicate costs, incompatible periods or an assumption that was mistaken for an observation.
Copy the source value at its available precision and postpone rounding until the displayed result needs it. If an input is uncertain, do not replace it with a silent average: enter a named base case and preserve a defensible low and high case for later comparison. Give each scenario a short label so screenshots, exported notes and later recalculations can be matched to the correct assumptions without relying on memory. The Time-of-Use Electricity Cost Calculator uses the values supplied to it; it does not retrieve a missing price, measurement, policy, route, tariff, scientific constant or professional decision unless the calculator explicitly says that it does.
Test how the electricity tariffs result changes
Reproduce “Worked case: baseline month” first and check every intermediate step against the written calculation. Then replace the example with your own input ledger without changing the equation or unit convention. Next reproduce “Worked case: shift 40 kWh off peak” as a genuinely different use case. Working through both cases matters because a formula that appears obvious in one direction can expose a denominator, rounding, calendar, sign or allocation error when the scenario changes.
Use the Time-of-Use Electricity Cost Calculator comparison table as a sensitivity test, not as decoration. Keep the calculation question fixed, change one material driver, and write the resulting difference in both absolute and relative terms when both are meaningful. If several inputs are uncertain, change them one at a time before combining them into a stress case. That sequence shows which assumption drives the answer and avoids attributing a multi-input change to the wrong cause.
Reconcile the electricity tariffs answer independently
A calculator result should survive a reverse or component check. Rebuild the answer from the displayed intermediate values, substitute the result back into “charge = Σ(period kWh × period rate)”, and confirm that totals, shares, ranges or endpoints return to the entered record apart from final display rounding. Where the result involves whole packages, dates, route segments, rubric weights or billing tiers, reconcile the continuous calculation before applying the real-world rounding or boundary rule.
Keep the limitation beside the number rather than in a forgotten note. In this guide, the central boundary is: The calculator models entered peak/off-peak energy rates only. Taxes, fixed charges, demand charges, minimum bills, holidays and live utility rules are excluded unless represented elsewhere. A result can be numerically correct while remaining unsuitable for a decision because the source data is stale, the model omits a material condition, or the required legal, safety, clinical, engineering, academic or provider rule was never entered. Record that unresolved condition explicitly instead of treating extra decimal places as confidence.
Save and update a reproducible electricity tariffs scenario
Save the calculation date, the Time-of-Use Electricity Cost Calculator name, equation, complete input ledger, intermediate outputs, final result and rounding convention together. Also retain the reviewed reference “U.S. Department of Energy — Evaluating utility rate options” and the source or document used for every real-world input. This creates a small audit trail that another reader can reproduce without guessing which price, measurement, time zone, grading policy, physical model or operating condition supported the headline answer.[1]
Recalculate when a material input or governing rule changes; editing the old headline alone breaks the audit trail. Use Electricity Bill Estimator and Peak Demand Reduction Calculator for the adjacent questions they are designed to answer, while keeping the Time-of-Use Electricity Cost Calculator as the canonical workflow for this article. Separate calculator records make changes easier to trace and prevent one oversized worksheet from mixing calculations with different denominators, time bases or decision boundaries.
A practical audit checklist
- Current tariff and season confirmed
- Interval energy reconciled
- Total kWh preserved for pure shift
- Other bill components listed
- Operational constraints checked
Practical questions
Frequently asked questions
Is every off-peak kWh a saving?
Only relative to when it would otherwise occur and under the applicable rates.
What about demand charges?
They require a separate maximum-kW model and can change the result.
Can I use average monthly kWh?
Not to allocate time bands accurately; interval or defensible schedule data is preferable.
Further reading
Authoritative sources
Use these primary and professional resources to check definitions, conventions, or requirements that may extend beyond this guide.