Electricity Cost Calculator

Add up to four appliances by watts, hours per day, days per month and duty cycle to get kWh per day and month and the cost at your own flat $/kWh rate.

Interactive calculator · Method ELECTRICITY-COST-1.0 · Last reviewed: 2026-11-04

Calculate your scenario

For each appliance, kWh per day = watts × quantity × hours per day × duty cycle ÷ 100 ÷ 1,000, and kWh per month = kWh per day × days used per month.

Your inputs

Try an example

Appliance 1 power (example: refrigerator; 0 = unused) (W)

Appliance 1 hours per day (h)

Appliance 1 days used per month (days)

Appliance 1 duty cycle (share of on-time at full power) (%)

Appliance 1 quantity (units)

Appliance 2 power (example: TV; 0 = unused) (W)

Appliance 2 hours per day (h)

Appliance 2 days used per month (days)

Appliance 2 duty cycle (share of on-time at full power) (%)

Appliance 2 quantity (units)

Appliance 3 power (example: LED bulbs; 0 = unused) (W)

Appliance 3 hours per day (h)

Appliance 3 days used per month (days)

Appliance 3 duty cycle (share of on-time at full power) (%)

Appliance 3 quantity (units)

Appliance 4 power (example: unused; 0 = unused) (W)

Appliance 4 hours per day (h)

Appliance 4 days used per month (days)

Appliance 4 duty cycle (share of on-time at full power) (%)

Appliance 4 quantity (units)

Electricity rate (example 0.15) ($ per kWh)

Fixed monthly charge (example 0) ($ per month)

Default worked example. Edit the inputs to calculate your scenario.

Default worked example

Monthly cost $9.54

Annual cost (× 12) $114.48

Energy per month 63.6 kWh

Energy on a day all rows run 2.12 kWh

Energy charge per month (before fixed charge) $9.54

Largest monthly user Appliance 1 (59.4% of kWh)

kWh/month = Σ watts × qty × hours × duty ÷ 1,000 × days = 63.6 kWh; × $0.15/kWh = $9.54 + $0.00 fixed = $9.54 a month, $114.48 a year.

How to use the calculator

For each appliance enter its power in watts, how many hours a day it is switched on, how many days a month, the share of that time it actually draws full power (100% for steady loads), and how many you have. Then enter the rate from your bill and any fixed monthly charge.

What the result means

A refrigerator (150 W running 35% of the time), a 100 W TV for 5 hours and six 10 W bulbs for 6 hours use 2.12 kWh a day, 63.6 kWh a month, or $9.54 a month at an example $0.15/kWh.

Formula and units

For each appliance, kWh per day = watts × quantity × hours per day × duty cycle ÷ 100 ÷ 1,000, and kWh per month = kWh per day × days used per month. Monthly cost = total monthly kWh × your rate per kWh + the fixed monthly charge; annual cost = monthly cost × 12.

Worked examples

Fridge, TV and six LED bulbs: Appliance 1 power (example: refrigerator; 0 = unused): 150 W; Appliance 1 hours per day: 24 h; Appliance 1 days used per month: 30 days; Appliance 1 duty cycle (share of on-time at full power): 35 %; Appliance 1 quantity: 1 units; Appliance 2 power (example: TV; 0 = unused): 100 W; Appliance 2 hours per day: 5 h; Appliance 2 days used per month: 30 days; Appliance 2 duty cycle (share of on-time at full power): 100 %; Appliance 2 quantity: 1 units; Appliance 3 power (example: LED bulbs; 0 = unused): 10 W; Appliance 3 hours per day: 6 h; Appliance 3 days used per month: 30 days; Appliance 3 duty cycle (share of on-time at full power): 100 %; Appliance 3 quantity: 6 units; Appliance 4 power (example: unused; 0 = unused): 0 W; Appliance 4 hours per day: 4 h; Appliance 4 days used per month: 30 days; Appliance 4 duty cycle (share of on-time at full power): 100 %; Appliance 4 quantity: 1 units; Electricity rate (example 0.15): 0.15 $ per kWh; Fixed monthly charge (example 0): 0 $ per month.
Example result: Monthly cost: $9.54; Annual cost (× 12): $114.48; Energy per month: 63.6 kWh; Energy on a day all rows run: 2.12 kWh; Energy charge per month (before fixed charge): $9.54; Largest monthly user: Appliance 1 (59.4% of kWh).

Two 1,500 W space heaters in winter: Appliance 1 power (example: refrigerator; 0 = unused): 1500 W; Appliance 1 hours per day: 6 h; Appliance 1 days used per month: 20 days; Appliance 1 duty cycle (share of on-time at full power): 50 %; Appliance 1 quantity: 2 units; Appliance 2 power (example: TV; 0 = unused): 0 W; Appliance 2 hours per day: 5 h; Appliance 2 days used per month: 30 days; Appliance 2 duty cycle (share of on-time at full power): 100 %; Appliance 2 quantity: 1 units; Appliance 3 power (example: LED bulbs; 0 = unused): 0 W; Appliance 3 hours per day: 6 h; Appliance 3 days used per month: 30 days; Appliance 3 duty cycle (share of on-time at full power): 100 %; Appliance 3 quantity: 6 units; Appliance 4 power (example: unused; 0 = unused): 0 W; Appliance 4 hours per day: 4 h; Appliance 4 days used per month: 30 days; Appliance 4 duty cycle (share of on-time at full power): 100 %; Appliance 4 quantity: 1 units; Electricity rate (example 0.15): 0.22 $ per kWh; Fixed monthly charge (example 0): 10 $ per month.
Example result: Monthly cost: $49.60; Annual cost (× 12): $595.20; Energy per month: 180 kWh; Energy on a day all rows run: 9 kWh; Energy charge per month (before fixed charge): $39.60; Largest monthly user: Appliance 1 (100% of kWh).

Limitations and common mistakes

Flat single-rate tariff only: time-of-use, tiered blocks, demand charges, taxes and fees beyond the fixed charge you enter are not modeled, and the default rate is an example. Nameplate watts are often the maximum draw; a meter reading or the duty cycle gives a better estimate for cycling loads such as refrigerators and heaters. Standby power counts only if you add it as a row.

Using a refrigerator's or space heater's rated watts for 24 hours at 100% duty; their compressors and elements cycle, so the real energy is much lower.

Sources and assumptions

Method ELECTRICITY-COST-1.0; last formula review 2026-11-04. Sources and their supported claims. Calculation methodology.