Fixed vs Variable Gas Rates: What Does the Price Lock Cover?
Compare fixed vs variable gas rates, price-lock periods and supply charges. Learn why fixed rates, fixed terms and equal monthly bills mean different things.
CompareUs Editorial TeamConsumer utilities editorial team
Fixed vs variable gas rates can be confusing because energy offers use “fixed” to describe several different things. A fixed unit price, a fixed contract period and a regular monthly payment are not the same promise. Before choosing, find the clause that says what the retailer can change.
Quick answer
Fixed vs variable gas rates is a choice about price certainty, not a guarantee of a fixed bill. Check exactly which rates are protected, for how long and under what exceptions. Compare the full cost at your expected usage, including supply charges, before paying a premium for certainty or choosing a variable offer.
Fixed vs variable gas rates: separate four promises
Energy Made Easy warns that a fixed-term energy plan does not necessarily have fixed prices. The useful question is not whether the advertisement contains the word “fixed”, but which part of the bill the contract protects.
| Description | What it can mean | What it does not establish |
|---|---|---|
| Fixed usage rate | Specified cents per MJ protected for a period | A constant total bill |
| Fixed supply charge | Specified daily connection price protected | Protection for every other fee |
| Fixed benefit period | A discount or benefit has a stated duration | That underlying rates cannot change |
| Equal instalments | Payments are smoothed across the year | That actual consumption costs are capped |
Read the rate schedule together with the general terms. If one document appears to contradict another, ask the retailer to identify the applicable offer in writing before you sign up.
A current product example, not a national recommendation
On 28 September 2026, EnergyAustralia’s Rate Fix FAQs described twelve-month protection for electricity and gas usage rates and daily supply charges. The contract itself is ongoing. The page also explains that both increases and decreases are excluded during the protected period, and identifies a meter-type change exception.
By contrast, EnergyAustralia’s Flexi Plan information describes variable electricity and gas rates with a twelve-month discount benefit. That illustrates why a benefit period should not be mistaken for fixed underlying prices. Confirm the current offer, eligible fuel, location and discount calculation in the address-specific documents.
These examples establish that the distinction exists; they are not a whole-market ranking or a statement that either product is available at every address. No actual tariff rate is quoted here because the appropriate comparison requires your property and gas consumption.
Check the boundaries of the guarantee
Record the start and end dates, the protected usage blocks and the protected daily supply charge. Ask whether taxes, regulated pass-through charges, payment fees or special meter services are included or excluded. Do not assume a “price lock” covers everything on the invoice.
Also check what happens if you move, change the meter arrangement or alter the plan. A guarantee attached to one offer at one address may not simply transfer to another property. Ask about cancellation conditions separately from the price-protection period.
Our gas tariff guide explains usage and supply components. Use it to identify the prices being protected before comparing promotional wording.
Calculate the premium for certainty
Suppose a hypothetical fixed offer charges $1.00 per day and 4.0 cents per MJ, while a hypothetical variable offer starts at $0.95 per day and 3.7 cents per MJ. At 25,000 MJ over 365 days, the fixed offer costs $1,365 and the variable offer costs $1,271.75 before any other charges or benefits.
The starting difference is $93.25 for the year. That is the illustrative premium for certainty if the variable rates do not change. It is not a forecast, a market average or a quote from the retailer examples above.
If the variable supply charge stayed at $0.95, its usage-weighted average rate would need to reach about 4.073 cents per MJ for the two totals to match. The calculation is ($1,365 − $346.75) ÷ 25,000. A midyear change must be applied to the gas actually used after the change, not automatically to half the annual consumption.
Winter usage makes timing important
Gas heating can concentrate consumption in colder months. A rate change before a heavy-use period may have a different effect from the same change after winter. Use bill history where possible rather than dividing annual usage into twelve equal pieces.
Keep price scenarios separate from consumption scenarios. One test might hold usage constant and vary prices. Another might allow for a colder winter or an extra household member. Mixing both changes without labelling them makes it hard to see which assumption drives the result.
The gas cost calculator can help with a usage-based estimate. For tiered prices, seasonal blocks or changing rates, check that the method reflects the actual tariff rather than treating every MJ as having one price.
Predictable payments are a separate tool
If the main concern is a large winter invoice, ask about payment smoothing as well as price structure. Regular instalments can make cash flow easier to manage, but the account still needs reconciliation against actual charges. A low instalment is not evidence of a cheap annual plan.
Ask when the amount is reviewed, whether debit or credit balances are carried forward and what happens on cancellation. Keep enough information to distinguish a price increase from an adjustment because earlier instalments did not cover consumption.
If affordability is already a problem, contact the retailer’s payment-assistance team. A fixed-rate offer is not a substitute for a sustainable payment arrangement or a review of eligible support.
Plan for the end of the protected period
Set a reminder before the guarantee ends. Request the rates and conditions that will apply afterwards and compare them with available alternatives. Do not assume another twelve-month guarantee renews automatically, or that the account closes when the original benefit expires.
Retain the original offer and any price-change notice. If a billed rate appears inconsistent with the guarantee, identify the specific charge and date when asking for an explanation. A clear record is more useful than a screenshot of a promotional headline alone.
Make the final choice on total cost and comfort with risk
A household may prefer a modest, clearly understood premium for certainty. Another may prefer a lower starting variable price and regular reviews. Neither preference removes the need to check the whole bill, the actual guarantee and the ability to change plans.
Use gas comparison with your address and annual consumption once the terms are clear. The CompareUs Editorial Team’s examples are arithmetic illustrations, not predictions of future gas prices. Keep the decision tied to what is offered to your household today.
Where should you go next?
FAQs
Does a fixed gas rate mean my bill cannot rise?
No. A fixed rate protects specified prices, not the amount of gas consumed or the number of billing days. Colder weather or more hot-water use can still increase the bill. Other fees may sit outside the guarantee.
Is a twelve-month benefit period a price guarantee?
Not by itself. It may describe a discount or another benefit while the underlying rates remain variable. Read the price-change clause and the offer’s rate table rather than relying on the duration in a headline.
Can I get a fixed-price gas offer?
Some retailers advertise fixed-rate products, but availability depends on the address and current offer. EnergyAustralia’s Rate Fix is one official example checked for this guide. Obtain current gas documents for your property before assuming eligibility.
What happens if variable rates fall?
A fixed offer may not automatically follow the reduction. Whether changing plans makes sense depends on the new rates, remaining guarantee period and any applicable conditions or costs. Ask the retailer rather than assuming the lock only protects against increases.
Does equal monthly billing fix my gas price?
No. A payment-smoothing arrangement can collect similar instalments while actual usage and rates determine the eventual account balance. Ask how payments are reviewed and whether a catch-up amount can arise.
Which option is cheaper?
There is no universal winner. Compare the same consumption and supply period, then test plausible changes without treating them as forecasts. A fixed offer can be worth considering for certainty while still costing more than a variable alternative.