That Old Refrigerator In Your Garage, Your Gaming PC Running 24/7, Your AC Unit Cranked All Summer-Do You Know How Much They're Actually Costing You?
Most people guess wrong. A 1,500-watt space heater running 8 hours daily might cost $40โ$60 per month, not the $5 or $20 many assume. This calculator cuts through the guesswork and shows you the exact monthly or annual cost of running any appliance, using your actual local electricity rate.
What This Calculator Does
This calculator converts an appliance's power consumption (in watts) and usage duration into electricity cost. You input the wattage (from the appliance's label or manual), how many hours per day you run it, your local electricity rate (from your utility bill), and the calculator instantly shows you hourly, daily, monthly, and annual costs. It also converts watts to kilowatt-hours (kWh)-the unit your utility charges you for-so you understand what's happening under the hood. The result helps you prioritize which devices to upgrade, replace, or use less frequently.
How to Use This Calculator
Start by finding the wattage of your appliance. Check the label on the back or bottom (older appliances often have this printed clearly), or look it up in the manual. If you can't find it, plug the appliance into a Kill-a-Watt meter (about $10โ$15) to measure real consumption. For central AC or furnace, check your manual or contact your HVAC installer for capacity in watts or BTU. Next, estimate daily usage hours-be realistic. If you leave a light on 6 hours per day, that's 6 hours. If your washer runs 1 hour, three times a week, that's 3 hours per week, or 0.4 hours per day. Finally, enter your electricity rate. Find this on your monthly bill in $/kWh. Most US rates are $0.10โ$0.20/kWh depending on region; some areas are as high as $0.30+. The calculator will show you daily, monthly, and annual costs in seconds.
The Formula Behind the Math
The math is simple but revealing:
Step 1: Convert watts to kilowatts
Kilowatts = watts รท 1,000
For a 1,500-watt space heater:
Step 2: Calculate daily kWh consumption
Daily kWh = kW ร hours per day
If the heater runs 8 hours daily:
Step 3: Calculate monthly kWh consumption
Monthly kWh = daily kWh ร 30 (or your exact days per month)
Step 4: Multiply by your electricity rate
Monthly cost = monthly kWh ร your $/kWh rate
At $0.15/kWh:
Annual cost = monthly cost ร 12 = $648/year
Our calculator does all of this instantly-but now you understand exactly what it's computing. The key insight: wattage and runtime are multiplied, so cutting either one in half cuts your cost in half. A 1,500-watt heater running 4 hours instead of 8 costs $27/month instead of $54.
Identifying Your Biggest Energy Drains
Run this calculator on several household appliances to spot patterns. Typically, the largest users are: air conditioning and heating systems (thousands of watts, running many hours), water heaters (4,000โ5,500 watts, cycling throughout the day), refrigerators (600โ800 watts, running 24/7 but not at full power), clothes dryers (3,000โ6,000 watts, 1โ2 hours per load), and space heaters (1,500 watts, often user-controlled). Gaming PCs, home servers, and always-on entertainment systems can also be significant. Laptops, phones, and small devices are usually negligible. Once you know the big offenders, you can make strategic upgrades or behavior changes.
Calculating True Appliance Operating Cost
If you're shopping for a new appliance, use this calculator to compare operating costs. A high-efficiency refrigerator might use 400 watts instead of 800, cutting cooling costs in half. An ENERGY STAR washer uses less water and electricity, with lower per-load costs. A heat pump water heater uses about 60% less energy than a traditional electric resistance tank. Over 10โ15 years, these efficiency gains often recoup the higher upfront cost, sometimes within 5 years. Factor both purchase price and operating cost into your decision.
Demand Charges and Peak Pricing
Most residential customers pay a simple $/kWh rate. However, some utilities charge higher rates during peak hours (typically 2โ9 PM on weekdays) and lower rates during off-peak hours. If your utility has time-of-use rates, you can lower costs by shifting flexible loads (dishwasher, laundry, EV charging) to off-peak hours. Some commercial customers also face demand charges-a penalty if your peak instantaneous draw exceeds a threshold. This calculator uses average rates; if you have time-of-use pricing, run separate calculations for peak and off-peak usage.
Plug Loads and Phantom Power
Every plugged-in device draws some power, even when "off." Your cable box, gaming console, microwave clock, and cell phone charger consume 5โ50 watts each continuously. A home with 20 such devices might waste 100โ500 watts idle. Over a month, that's 72โ360 kWh of "vampire power." Cost: $10โ$50/month. Use power strips to kill entire categories of phantom draw, or unplug chargers and devices you're not actively using.
Tips and Things to Watch Out For
Nameplate wattage is maximum, not average. The label says "1,500 watts," but thermostats and variable-speed devices cycle or adjust output. Refrigerators, for example, cycle on and off throughout the day and use far less than their rated wattage on average. For these, either measure with a meter or use typical usage estimates (online databases have average real-world consumption for common appliances).
Electricity rates vary by region and season. Your rate might change monthly or have summer and winter tiers. Use your most recent bill or an annual average. If rates are rising, future costs will be higher than this calculator suggests.
High-wattage seasonal devices skew costs. A 5,000-watt pool pump running 4 hours daily for 6 summer months costs about $360 in electricity alone. An air conditioner cycling through a hot summer can easily add $300+ to monthly bills. Budget seasonal surges separately.
Efficiency ratings don't always mean lower wattage. An "efficient" space heater still uses 1,500 watts if that's what you set it to; the efficiency means it heats more evenly or loses less to waste. Check actual wattage, not just the efficiency label.
Always-on devices add up fast. A 200-watt always-on device running 8,760 hours/year at $0.15/kWh costs $262/year. That's huge for something you don't think about. Identify and reduce always-on draw first.
Newer doesn't always mean efficient. An older refrigerator might use 800 watts; a new one uses 400 watts. But a ten-year-old LED light uses similar watts to a new one. Context matters; replace the actual energy hogs, not everything old.
Frequently Asked Questions
What's an average kWh rate in the US?
The national average is about $0.15/kWh as of 2026, but varies from $0.10 in cheap-electricity states (Louisiana, Oklahoma) to $0.28+ in expensive states (Massachusetts, Hawaii). Check your bill to know your rate.
Why is my AC bill so high in summer?
Air conditioning is one of the largest single loads in most homes, often 3,000โ5,000 watts running 8โ12+ hours daily. A single degree of thermostat adjustment can cut AC runtime by 10โ15%, saving $20โ$50/month.
How much does it cost to leave a light on all day?
A traditional 60-watt incandescent bulb running 24 hours daily uses 1.44 kWh/day. At $0.15/kWh, that's $0.22/day or $80/year. An LED (9 watts) costs $0.03/day or $12/year. This is why LED switches matter.
How much does a 1,500-watt space heater cost to run?
At 8 hours daily and $0.15/kWh: 1.5 kW ร 8 hrs ร 30 days ร $0.15 = $54/month, or $648/year. Central heating is usually cheaper per BTU delivered, but space heaters are effective for zone heating.
Does unplugging things really save money?
Every 100 watts of phantom load costs about $13/month. If you have 10 devices at 30 watts each, that's $39/month. Unplugging is free and worthwhile.
Should I replace old appliances just to save on electricity?
Only if the payback is realistic. A $1,000 refrigerator saving $100/year takes 10 years to break even, and the old one still works. Replace when the appliance fails, or if the annual operating cost is higher than financing a new one.
How does pool/spa heating cost?
A pool heater (30,000โ100,000 BTU) uses 3,000โ7,000 watts and might run 4โ8 hours daily. Monthly costs: $180โ$840 depending on heater type and runtime. Solar pool heaters or heat pumps reduce this significantly but have upfront costs.
How do I compare utility rates between providers?
Use this calculator to estimate a typical monthly bill, then multiply by the supplier's rate. Some regions allow choice of suppliers; others don't. Compare not just price but also contract length and terms.
Related Calculators
Use the Electricity Bill Calculator to forecast your total monthly bill from multiple appliances running simultaneously. The LED Savings Calculator shows exactly how much switching from incandescent to LED saves per year. The Electric vs. Gas Cost Calculator helps you decide whether a gas or electric appliance is cheaper to operate long-term.