Diagnostic · 7 min read
Why is my electric bill so high this month? A diagnostic walkthrough
Nine times out of ten, a surprise bill traces back to one of six causes. Work through them in order of likelihood and the answer usually falls out in about ten minutes.
Start by separating rate from usage
An electric bill has two moving parts: how many kWh you used and what each kWh cost. A bill can jump because usage went up, because the per-kWh rate went up, or because both moved at once. Before diagnosing anything else, pull last month's bill and this month's side by side and write down four numbers: kWh used, supply rate in cents per kWh, delivery rate in cents per kWh, and the total.
If kWh is flat but the total jumped, the cause is on the rate side and you can skip to cause #2. If kWh is up, work through the causes in the order below.
Key insight
The four numbers that matter on any bill.
Cause 1: Weather drove a higher duty cycle
This is the single most common cause and it's the first place to look. Heating and cooling are 60-70% of the average home's electric bill in peak months. A summer where average temperatures run 5°F hotter or a winter that hits a two-week cold snap can push HVAC runtime up 30-50% without you changing a thermostat setting.
The math: a 3,500W central AC running 8 hours a day at 16.5¢/kWh costs about $139 a month. Same AC forced to run 12 hours during a heat wave costs $208. That's a $69 jump with no behavior change. How to check: compare this month's average outdoor temperature to the same month last year. Most utilities now show a degree-day chart right on the bill.
Cause 2: The supply or delivery rate changed
Utility rates move. Supply rates (what the power itself costs) reset every six months in many states and can swing 20% either way depending on natural gas prices. Delivery rates reset on a slower cadence but still step up annually in most markets. A 2¢/kWh rate change on a house using 1,000 kWh a month is $20 extra. On a house using 2,500 kWh, it's $50.
How to check: find last month's supply and delivery rates on the old bill and compare to this month's. If either moved, multiply the delta by your kWh to get the dollar impact. See current rates for every state on the state rate pages to sanity-check whether your number is reasonable for your region.
Cause 3: A new high-draw appliance entered the house
Anything that pulls more than 1,000 watts for extended hours can visibly move a bill. The usual suspects:
- A space heater at 1,500W for 10 hours a day adds about $56 a month.
- A hot tub running year-round adds $40-100 a month depending on insulation and setpoint.
- A new EV charging at home adds $30-60 a month for a typical commute.
- A second window AC in a bedroom adds $20-40 a month in summer.
How to check: walk through the house and list anything that wasn't plugged in this time last year. Anything with a compressor, heating element, or motor is a candidate.
Cause 4: An old appliance is drifting inefficient
Appliances don't fail all at once. They drift. A fridge with a bad door seal or a dusty condenser coil can pull 30-40% more than its nameplate. An old HVAC system losing refrigerant runs longer to hit the same setpoint. A water heater with mineral buildup heats slower and cycles more. The bill moves quietly over months until you look at a year-over-year comparison.
How to check: pull your last 12 months of bills from the utility portal. If kWh is creeping up 5-10% year over year with no lifestyle change, something is drifting. Prime suspects are the oldest motorized or heat-element appliances in the house: fridge, HVAC compressor, water heater, pool pump.
Cause 5: Usage patterns shifted
A new baby adds roughly 50-80 kWh a month in laundry, warm baths, and lights. A partner switching to remote work pushes the daytime thermostat from 78°F to 72°F in summer, which is worth $30-50 a month on a central AC. Houseguests for two weeks can run the dishwasher daily instead of twice a week. None of these feel like big changes. All of them show up on the bill.
How to check: think about what changed at home in the last 60 days. Work schedule, family size, guests, a pet that needs the house warmer, kids home from school. Map each change to an appliance and estimate the extra runtime.
Cause 6: Broken meter or billing error
This is the last place to look because it's the rarest, but it does happen. A smart meter can fail in a way that over-reports usage. An estimated read (the utility guesses instead of pulling an actual number) can catch up months later with a big correction. A previous tenant's final bill can get rolled onto yours if the handoff was sloppy.
How to check: look for the word "estimated" on recent bills. Read the meter yourself and compare to what's printed. If the numbers don't match, call the utility and request an on-site reread. Most utilities will send a tech within a week and credit any confirmed error.
Run the numbers on the suspect
Once you have a candidate, plug the real wattage and runtime into the calculator below. If the math lines up with your bill increase, you've found it. If not, move to the next cause on the list.
Estimated cost
A space heater draws full power only while the thermostat/compressor is running — about 7.5 effective hours at 1500W across your 10-hour window.
What actually moves the bill back down
Weather is out of your hands. Rate changes are out of your hands. The three causes you can act on are new appliances (swap or schedule), drifting old appliances (maintain or replace), and usage shifts (adjust setpoints or timing). The biggest single lever in most homes is the HVAC setpoint: every 1°F closer to the outdoor temperature is worth roughly 6-8% on the heating or cooling bill. That's a free change and it compounds every month of the season.