Why a bill suddenly jumps
| Cause | What happened |
|---|---|
| Catch-up bill | Several low estimated bills were followed by an actual read, so the difference all landed on one bill. |
| Back-billing | The retailer found it had undercharged you, for example after a meter or tariff error. |
| Price rise | New rates started part way through the billing period, usually on 1 July. |
| Discount or benefit ended | A fixed-term benefit ran out and your rates moved up. |
| Extreme weather | A heatwave or cold snap pushed heating or cooling use up for weeks. |
| Switching overlap | A final bill from your old retailer and a first bill from your new one arrived close together. |
Rules that protect you
- Back-billing limit: where you were undercharged through no fault of yours, the retailer can generally only recover the amount for the 9 months before it notified you, cannot charge interest, and must offer to let you pay it off over time.
- Price change notice: retailers must tell you before your prices change. Since 1 July 2026, retailers in NSW, Queensland, South Australia, Tasmania and the ACT can raise market prices only once every 12 months.
- Benefit periods: since 1 July 2026 in the same states, if a plan's benefits change or expire you pay no more than the standing offer price.
- Disputed amounts: while a complaint about the bill is unresolved, you generally only need to pay the part not in dispute, and cannot be disconnected over the disputed amount.
What to do when a big bill arrives
Do not ignore it
Contact your retailer before the due date, even if you cannot pay yet.
Check what caused it
Look at the read type, the dates, the rates and the kWh a day. Our high bill guide walks through each check.
Ask for time or a payment plan
Retailers can extend the due date or spread the amount over several payments.
Ask about hardship help
If you are struggling, your retailer must tell you about its hardship program.
Escalate if needed
If the bill seems wrong and the retailer will not fix it, contact your energy ombudsman.
Stop it happening again
Bill smoothing spreads costs into equal payments, a smart meter ends estimated reads, and checking your plan each year catches ended benefits early. See billing periods.
Questions about bill shock
Most often because estimated bills were too low and an actual read caught up, because prices rose part way through the period, because a discount ended, or because of an unusually hot or cold quarter.
If you were undercharged through no fault of your own, the retailer can generally only recover the amount for the 9 months before it told you, cannot charge interest, and must offer instalments.
Contact your retailer before the due date. Ask for an extension, a payment plan or its hardship program. You cannot be disconnected while you keep to an agreed plan.
Yes. Raise it with your retailer first, then the energy ombudsman. You generally only need to pay the part that is not in dispute while the complaint is open.
Sources
Every rate on this page comes from the regulator or the regulated retailer. Last checked October 2026. Prices include GST unless we say otherwise.