How to calculate what your heating really costs per day
Published 17 October 2026 · SepoooTools blog
The heating season has started, and most of us only see the cost weeks later, on the bill. That is too late to change anything. The good news: you can work out your heating cost for a single day with one line of math. You need two numbers, and both are on your bill.
Why people are asking about this now
In early October 2026 the U.S. Energy Information Administration (EIA) published its winter outlook for November to March. It expects households that heat mainly with heating oil to spend about 21% more than last winter, and homes with electric heating about 4% more. Homes using natural gas are expected to spend about 9% less, and propane about 3% less.
Those are national averages for the United States. Your bill can be very different, and prices differ in every country. That is exactly why it helps to do the math with your numbers.
The one formula you need
Cost per day = energy used per day × price per unit
Energy is usually measured in kWh (kilowatt hours). Electricity is billed in kWh almost everywhere. In many countries gas is billed in kWh too. Your bill shows the unit price, for example "0.32 per kWh". Use that number, not the monthly payment, because the monthly payment also includes fixed fees.
Method 1: an electric heater (watts to kWh)
Every electric heater has a label with its power in watts (W). Here are the steps:
- Find the watts on the label, for example 1500 W.
- Divide by 1000 to get kilowatts: 1500 ÷ 1000 = 1.5 kW.
- Multiply by the hours you run it: 1.5 kW × 5 hours = 7.5 kWh per day.
- Multiply by your price: 7.5 kWh × 0.35 = 2.63 per day (rounded).
- For a month of 30 days: 2.625 × 30 = 78.75.
The price of 0.35 here is only an example. Put in your own price and the result changes with it.
One honest note: the label shows the maximum power. Many heaters have a thermostat and switch off for a while when the room is warm. So the real number is often a bit lower than this result. Think of it as the upper limit.
| Heater | Hours per day | kWh per day | Cost at 0.30/kWh |
|---|---|---|---|
| 500 W oil radiator | 3 | 1.5 | 0.45 |
| 1500 W fan heater | 5 | 7.5 | 2.25 |
| 2000 W convector | 3 | 6.0 | 1.80 |
| 2000 W convector | 8 | 16.0 | 4.80 |
Method 2: read your meter (the most accurate way)
Formulas are useful, but your meter shows what really happened. This works for electricity and for gas.
- Read the meter today at, say, 8 a.m. Write down the number. Example: 12,340.
- Read it again tomorrow at 8 a.m. Example: 12,352.
- The difference is what you used in one day: 12,352 − 12,340 = 12 kWh.
- Multiply by your price: 12 × 0.32 = 3.84 for that day.
Do this on a cold day and on a mild day. The gap between the two shows you how much the weather really moves your bill. A photo of the meter with your phone is the easiest way to keep the readings.
If your gas meter shows cubic metres
Some gas meters count in m³, not kWh. Your bill then prints a conversion factor. In Germany, for example, the bill shows a "Brennwert" and a "Zustandszahl". You multiply: m³ × Brennwert × Zustandszahl = kWh. After that, use the same formula as above. In the U.S. gas is often billed in therms. One therm is about 29.3 kWh.
Method 3: heating oil or pellets
Here you do not pay per day. You fill a tank. The math is still simple:
Cost per day = (litres or gallons used ÷ number of days) × price you paid per litre or gallon
Check the tank level on two dates, a week apart. If 70 litres went in 7 days, that is 10 litres per day. At 1.10 per litre, heating cost you 11.00 per day. (Example numbers. Use your delivery invoice for the price.)
Turning a percentage rise into money
News reports often give a percentage, like the 21% for heating oil. To see what that means for you, multiply last winter's cost by 1 plus the percentage. If you paid 1,000 last winter: 1,000 × 1.21 = 1,210. That is 210 more. Treat it as a rough guide, because your own usage and your own prices count more than any average.
Common mistakes
- Using the monthly payment as the price. The monthly payment includes fixed fees. Use the price per kWh.
- Forgetting to divide by 1000. 1500 W is 1.5 kW, not 1500 kW.
- Mixing net and gross prices. Some contracts show the price without tax. Use the price you really pay.
- Counting only one cold day. Average a few days, or a whole week, before you decide anything.
A small tool idea
We are thinking about a tiny heater cost calculator: enter watts, hours and your price, and get the cost per day, month and season. Until then, the formula above does the same job on any phone calculator.
Questions people ask
How much does a 1500 watt heater cost per hour?
It uses 1.5 kWh per hour. Multiply 1.5 by your price per kWh. At 0.30 per kWh that is 0.45 per hour, in your own currency.
Where do I find my price per kWh?
On your latest electricity or gas bill, or in your contract. Use the unit price, not the monthly total, because the total also contains fixed fees.
Is a plug-in heater cheaper than central heating?
It depends on your prices and how you use them. A small heater in one room for a short time can cost less than heating a whole flat, but for many hours a day it often costs more. Do the math with your own numbers.
Changing your clocks next week? Our guide on the clock change on 25 October 2026 explains the new time differences. And for photos, PDFs and file sizes, all our free tools are on the tools page. They work in your browser, and your files are never uploaded.
Source for the winter outlook: U.S. Energy Information Administration, Short-Term Energy Outlook, Winter Fuels Outlook, October 2026. All example prices on this page are only examples, not price advice.