Electricity Cost Calculator

Estimate energy use and cost for one or more appliances, including optional standby power and a separately listed fixed monthly charge.

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How to Use the Electricity Cost Calculator

For each appliance, enter a name, active watts, quantity, daily active hours and days used in the selected month. Standby watts apply during the remaining hours of each usage day. Enter your variable price per kWh and a currency label. Add a fixed monthly charge if needed. Save a comparison baseline before changing wattage or hours to see the monthly energy difference.

Formula and Explanation

Daily kWh = quantity × (active watts × active hours + standby watts × (24 − active hours)) / 1,000
Monthly kWh = daily kWh × entered usage days
Annual kWh = daily kWh × 365
Energy cost = kWh × price per kWh
Monthly total = monthly energy cost + fixed monthly charge
Annual total = annual energy cost + 12 × fixed monthly charge

The watts × hours / 1,000 formula is unchanged. Standby power is counted only outside the active hours, preventing double-counting. Daily totals represent one modeled usage day. Monthly totals use each appliance’s entered days, while the annual projection explicitly assumes the same daily pattern for 365 days, not twelve copies of the chosen month. Fixed charges appear separately and are not allocated to individual appliances.

Use measured average watts or equivalent active hours for cycling appliances. Actual tariffs, seasons, duty cycles, taxes, demand fees and time-of-use rates vary. A currency label does not perform currency conversion. Annual values are a 365-day projection; seasonal or occasional usage needs a separate scenario. Standby is not added on days outside entered monthly usage. Comparison baselines are temporary in-page values.

Worked Example

A 1,500 W appliance at 2.5 hours/day for 30 days, with quantity 1 and zero standby, uses 112.5 kWh/month. At 0.20 currency units/kWh, energy cost is 22.50. Its 365-day annual projection is 1,368.75 kWh and 273.75 in energy charges. A fixed monthly charge of 5 gives monthly total 27.50 and annual total 333.75. Changing the month to 28 usage days changes monthly energy to 105 kWh but leaves that stated annual assumption unchanged.

Frequently Asked Questions

How is standby power counted?

Standby watts apply to 24 minus the entered active hours on each modeled usage day. Active watts and standby watts are not both charged for the same hour. Enter zero standby when it is not known or not applicable.

Why is annual use not monthly use times twelve?

The monthly calculation uses each appliance’s entered usage days. The annual projection separately assumes 365 days of its daily pattern. This avoids silently treating a 28-day month as twelve identical months.

Does this match every electricity tariff?

No. Enter your own variable rate and label. The calculator models one rate and an optional fixed monthly charge; it does not implement tiered, time-of-use or demand pricing.

How does usage comparison work?

Save a valid scenario as the baseline, then edit hours, wattage or other inputs. The result shows the change in monthly kWh and energy cost. The baseline stays in memory until reset or page reload.