Why Is My Gas Bill So High?

A gas bill that lands at double or triple the last one feels like an error. Sometimes it is. More often, the bill is doing exactly what gas bills do, and nobody has ever explained how they actually work.

Most advice on this question is a single generic checklist written to cover electricity and gas at once. Gas deserves its own diagnosis, because gas is measured differently, billed differently and used differently. So here is the gas-specific version, in rough order of likelihood. Start at the top and work down. If the bill in your hand is an electricity bill, why is my bill so high is the equivalent walkthrough for that fuel.

Winter did it, and that is normal physics

For most Australian households, gas has two big jobs: heating and hot water. Both are seasonal. Space heating obviously runs in winter and barely exists in summer. Hot water is sneakier: in winter, the water coming into your system is colder, so it takes more energy to bring every litre up to temperature, and most of us shower longer and warmer too.

Because gas load is so dominated by these two jobs, a winter gas bill that is several times your summer bill is not evidence of a problem. It is the expected shape of the year. An electricity bill tends to wobble around a baseline; a gas bill in a heating household looks more like a mountain range, with one big peak every winter. If your alarming bill covers June and July, the first suspect is the season, and the season usually did it.

The honest test is never "is this bill bigger than the last one?" It is "is this winter's bill bigger than last winter's, per day, on the same plan?" We will come back to how to check that.

Your previous bill may have been a guess

Here is the quirk that catches more people than any other. Gas meters are physically read by a person roughly every two months in most areas, but many retailers bill more often than that. The result: some of your bills are based on an actual meter read, and the ones in between are estimates, calculated from your past usage.

Your bill says which kind it is. Look for the words "actual" or "estimated" next to the meter read, sometimes abbreviated to a single letter such as A or E. If you are not sure where to find it, the line-by-line gas bill guide points at the exact block.

Why does this matter for a high bill? Because an estimate can undershoot. If your usage crept up, say a new heater, a colder snap, an extra person in the house, the estimated bill quietly charges you for less gas than you actually burned. Then the next actual read arrives, the meter tells the truth, and the catch-up lands in one bill. That bill looks like a spike. It is really a correction: gas you used across two periods, billed in one.

So before you panic at a big bill, check the read type on it and on the one before. A modest estimated bill followed by a large actual one is the classic pattern, and it means the problem is timing, not consumption.

Catch-up reads meet stepped rates

There is a second-order effect worth knowing. Many gas plans use stepped rates, sometimes called block tariffs: the first chunk of usage in a billing period is charged at one rate per megajoule, the next chunk at another, and so on. Residential gas rates by state sets out the two tariff shapes and where each one is common.

When a catch-up read pushes two periods' worth of usage into one billing period, more of that usage can land in different rate blocks than it would have if it had been measured evenly across the two periods. Depending on how your plan's blocks are structured, that can shift what you pay per megajoule for part of the gas. It is not a retailer doing anything improper; it is arithmetic falling out of the way estimates, actual reads and block structures interact. It is also one more reason a catch-up bill can look stranger than a simple "two periods in one" doubling.

Count the days before you compare anything

Billing periods are not all the same length. A 62-day bill and a 58-day bill differ by nearly a week of winter heating before anything else changes. Comparing the totals of two bills with different period lengths is comparing apples with a slightly bigger bag of apples.

The fix takes ten seconds: divide the total usage (and the total cost, if you like) by the number of days in the billing period, which is printed on the bill. Megajoules per day is the number that means something. Then compare it to the same season last year, not to the bill before this one. Winter against spring tells you nothing except that winter is cold.

A plan or rate change mid-period

If your rates changed part-way through the billing period, the bill will usually show two sets of charge lines: this many megajoules at the old rate, that many at the new one. A price change landing mid-winter, on a long billing period, compounds with everything above. It is worth a minute with the detail section of the bill to see whether the per-megajoule rates or the daily supply charge moved, and when.

The physical culprits: hot water faults and leaks

If the reads are actual, the per-day usage genuinely jumped, and the season does not explain it, look at the hardware.

The hot water system is the usual offender. A failing thermostat can keep the burner running longer than it should. A slow leak on the hot water line, including under a concrete slab where you will never see a puddle, forces the system to heat replacement water around the clock. A dripping hot tap does the same on a smaller scale.

There is a simple check. Turn off every gas appliance, make sure no hot tap is running, and watch the gas meter for a few minutes. If the dials or digits are still creeping, gas is going somewhere it should not, and it is time to call a licensed gasfitter. Persistent warm patches on a slab floor, or a hot water unit that seems to run constantly, point the same way.

The plan itself has drifted

Finally, the quiet one. A gas plan that was competitive when you signed up does not stay competitive by itself. Rates change, discounts and benefit periods expire, and better offers appear in the market without anyone ringing to tell you. Unlike electricity, gas has no regulated default price acting as a safety net underneath your plan, so there is no floor guaranteeing that doing nothing stays reasonable. Switching gas retailers covers what that means and how the transfer actually works.

If every other explanation on this list comes up empty, or even if the season explains the spike but the number still stings, the remaining question is whether you are paying more per megajoule and per day than you need to.

What to actually do

Four steps, in order:

1. Check the read type on this bill and the previous one. If this one is an actual read following an estimate, part of the spike is likely a correction, not new usage.
2. Divide by the billing days. Get your megajoules per day. Totals from different period lengths are not comparable.
3. Compare same season to same season. This winter's per-day usage against last winter's is the only fair fight.
4. Run the real bill through a complete-market comparison. Not a quote built on postcode averages, and not a panel of partnered retailers. Your actual usage, your actual rates, against every retailer in your state.

That last step is what Fix Your Bill does. We read your real bill and compare it against the whole market in your state using the public Consumer Data Right plan data, so the answer is about your house, not a hypothetical one. If your plan has drifted, you will see it in dollars. If it has not, you get something almost as valuable: the knowledge that the big bill was just winter, doing what winter does.