Why is my gas bill so high? 9 causes and how to check yours

Start here: is it usage, price or the bill itself?

Every high gas bill has one of three explanations. You used more gas, you paid more for each unit of gas, or the bill itself is unusual (longer than normal, estimated, or carrying a charge from an earlier period). They look identical on the total. They are easy to tell apart once you look at the right lines.

Put this bill next to the one from the same season last year, not the one from last quarter. Gas use is extremely seasonal, so a winter bill compared with an autumn bill will always look shocking. Then check three numbers on both: the number of days billed, the megajoules (MJ) used, and the price per MJ. Whichever moved is your answer.

If your usage went up

1. Heating

Gas space heating is the largest single gas load in most homes that have it, and it runs almost entirely in winter. A cold month, a new baby at home, someone working from home, or a ducted system set a few degrees higher will all show up as a large rise. See winter heating costs.

2. Hot water

Gas hot water runs all year, and in winter the cold incoming water makes it work harder. Longer showers, more people in the house or a storage tank set hotter than it needs to be all add up. See hot water running costs.

3. An ageing appliance

An old heater or hot water system can lose efficiency over time and burn more gas for the same heat. A storage hot water system that leaks, or a heater that needs a service, can quietly raise your usage for months.

4. A leak

Rare but important. If you smell gas, leave the house and call your gas distributor’s emergency line. If you only suspect it, turn off every gas appliance (including pilot lights), note the meter reading, and check it again a few hours later. If the number moved with everything off, have it checked.

If the price went up

5. A price change

Retailers can change the prices on a market offer, and must notify you before they do. If your usage in MJ is similar to the same bill last year but the dollars are higher, your rates moved.

6. Stepped (block) rates

Many gas plans charge one price for the first block of usage in a period and a different price above it. A big winter bill can push more of your usage into a different block. Check your bill for two usage lines at different prices.

7. A discount that stopped

A conditional discount, such as one for paying on time or by direct debit, disappears the moment the condition is missed. A benefit that applied for a set period can also end. Both make the same usage cost more overnight.

If the bill itself is unusual

8. More days

Gas meters are usually read every two or three months, and the dates move. A bill covering 98 days will be bigger than one covering 85 days at identical daily use. Divide the total by the days billed to compare fairly.

9. An estimated read, then a catch-up

If the meter reader could not get to your meter, the retailer estimates your usage. When a real reading finally happens, the difference lands on one bill. If the last bill was marked "estimated" and was low, this one may be making up for it. See how to read your meter and check the number yourself.

Why gas bills are measured in megajoules

Your gas meter measures volume, in cubic metres. Gas is sold by energy content, in megajoules. Your retailer converts one to the other using the heating value of the gas in your area and a pressure correction factor, both printed on the bill. You rarely need to check this calculation, but it explains why your meter reading and your billed MJ are different numbers.

For comparing bills, MJ per day is the number that matters. It removes the effect of a longer billing period and lets you compare winter with winter honestly.

Finding out if you are simply paying too much

Once you know why this bill is high, the remaining question is whether your gas plan is competitive. Gas plans vary widely, and households that have not compared in a few years are often paying well above the cheapest plan available at their address for exactly the same gas.

Upload your gas bill to EnergySorted and we read the usage, the period and your rates off it, then cost every gas plan available at your address against your real usage. We cover gas in Victoria, New South Wales, Queensland, South Australia and the ACT. Upload a few bills and we chart them side by side, so you can see whether your usage or your price is the thing that moved. Check your gas bill, or read how to save on your gas bill and what a typical gas bill looks like.