Recommended Free Tools
To estimate what an energy price increase will cost your household, use your own consumption, tariff rates and billing dates—not a headline “average bill.” For each fuel, multiply usage in every rate band by its unit price, add daily standing or supply charges for the exact number of days, include applicable fees and taxes, and subtract credits or discounts. Run that calculation once with the old prices and once with the new prices. The difference is the price shock, provided consumption and the number of days are held constant.
This method works for a gas bill, a single-rate electricity tariff, Economy 7 and other time-of-use plans. It also makes clear why a published price-cap average is not a personal bill forecast: the more energy you use, the more your bill changes.
As an Amazon Associate I earn from qualifying purchases.
The calculation that turns a rate change into a household cost
For each fuel and billing period, calculate:
Estimated cost = Σ (usage in each rate band × that band’s unit price) + (daily standing or supply charge × number of days) + applicable fees and taxes − credits or discounts
Then calculate the shock:
Estimated shock = new-price scenario cost − old-price scenario cost
#1 Best Overall
Use the same consumption and the same number of days in both scenarios. If you are budgeting for a year, model a full year on both sides. If you are checking one bill, use that bill’s actual start and end dates. This isolates the effect of prices from the separate effect of using more or less energy in winter, during a move or after a change in household size.
Ofgem describes unit rates as prices per kilowatt-hour (kWh) and standing charges as daily amounts. The Australian Energy Regulator (AER) uses the equivalent concepts of variable usage charges and fixed supply charges, with other fees and credits shown separately. Your bill may use different labels, but the arithmetic is the same.
Collect the figures before you calculate
Start with the bill or tariff document for the exact account you are modelling. Record the following items for the old and new scenarios where a change is proposed.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errors| Item | What to record | Why it matters |
|---|---|---|
| Usage | kWh for gas and electricity; for a multi-rate meter, kWh in each band | Usage is multiplied by the matching unit rate. |
| Unit rates | Old and new price per kWh for every band | A peak, off-peak or overnight band can have a different price. |
| Standing or supply charge | Old and new daily charge | This cost accrues even when consumption is zero. |
| Billing dates | Exact start and end dates, or the number of days | The daily charge depends on the period length. |
| Adjustments | Applicable taxes, fees, rebates, discounts, debt repayments and credits | These can change the amount actually paid without changing the unit rate. |
| Meter and tariff details | Tariff type, payment method, meter type and region | Published rates and eligibility can vary with each of these details. |
| Usage status | Actual meter reading or supplier estimate | An estimate introduces uncertainty that should be labelled in your scenario. |
Keep units consistent. A rate quoted in pence per kWh must be multiplied by kWh and then converted to pounds when you total a bill in pounds. A daily charge quoted in pence must likewise be converted after multiplying by the number of days.
Check whether the usage is measured or estimated
Look for “actual,” “meter read” or “estimated” beside each reading. The AER says estimated usage should be identified. If a reading is estimated, use the supplier’s figure as a provisional input, then rerun the estimate when an actual reading is available. Do not present an estimated-use result as a guaranteed bill.
Separate the old and new tariff documents
A price-change notice may show only the new unit rate while your previous bill shows the old one. Retrieve both figures, including each standing charge and each time-of-use band. A change in payment method or a new discount can otherwise be mistaken for a pure energy-price shock.
Step-by-step: calculate your old cost, new cost and shock
- Choose the period. Enter the bill dates or define a calendar year. Do not compare a 31-day bill with a 365-day estimate unless you are deliberately annualising both.
- Enter consumption by fuel. Put gas and electricity in separate rows. For Economy 7 or another multi-rate plan, create a row for every band, such as peak and off-peak.
- Apply the old unit rates. Multiply each old-band kWh figure by its old price. Add the band results for that fuel.
- Apply the new unit rates. Multiply the same kWh figures by the proposed prices. Keeping usage unchanged makes the difference a price scenario rather than a consumption forecast.
- Add fixed daily charges. Multiply each old and new standing or supply charge by the same number of days. Include separate charges for gas and electricity.
- Add or subtract account-level items. Include a fee, tax, rebate, discount, debt repayment or credit only if it applies to that household and period. If a policy adjustment is uncertain, create a separate scenario instead of silently including it.
- Subtract the old total from the new total. A positive result is an increase; a negative result is a reduction. Divide the result by the old total and multiply by 100 if you also need a percentage change.
A simple worksheet can have columns for fuel, rate band, kWh, old unit price, new unit price, old usage cost and new usage cost. Add standing charges and adjustments below the usage rows, then calculate the two totals. Keep the input cells for actual readings distinct from cells containing assumptions.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Single-rate shortcut and a worked example
For one fuel on a single-rate tariff, the change can be calculated directly:
Rank #2
- Ideal for Gifting
- Ideal for a bookworm
- Compact for travelling
Change = usage × (new unit rate − old unit rate) + days × (new daily charge − old daily charge)
This shortcut excludes other fees, taxes, credits and discounts, so add those separately when they change.
Hypothetical annual electricity example
Suppose a household uses 3,000 kWh of electricity in a year. The unit rate rises by 5 pence per kWh and the standing charge rises by 10 pence per day. The usage component is:
3,000 × £0.05 = £150
For a 365-day year, the fixed-charge component is:
365 × £0.10 = £36.50
The combined increase is £186.50 before any other adjustments. If you use 366 days for a leap-year budget, the fixed-charge component is £36.60 instead. These are arithmetic results from the stated hypothetical inputs, not a forecast or a typical household statistic.
Why the fixed charge can matter
The standing charge is independent of kWh. A low-use household therefore does not avoid the daily component, while a high-use household feels both the larger usage total and the same daily increase. Always show the two components separately so you can see which part of the shock is driving the result.
Time-of-use and multi-rate tariffs
Do not average peak and off-peak prices into one rate unless the supplier has already provided a valid weighted rate for your exact usage. Ofgem notes that multi-rate tariffs use different peak and off-peak prices.
- Read the meter or bill’s kWh for each band.
- Multiply peak kWh by the peak old rate and by the peak new rate.
- Repeat for off-peak, overnight or any additional band.
- Add the band totals, then add the daily supply charge and applicable adjustments.
If a household can move laundry, water heating or vehicle charging into a cheaper period, that changes the usage split. Model that as a separate consumption-pattern scenario; do not change the kWh split in the same calculation that is meant to isolate the price change.
The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Calculating a percentage change
After calculating both complete totals, use (new total − old total) ÷ old total × 100. Report the currency change as well. A percentage can look large when the old bill is small, while the absolute amount is what must be funded from the household budget.
Fees, taxes, rebates and credits
Energy bills often contain more than usage and standing charges. The AER identifies variable consumption charges, fixed supply charges, other fees and credits. For a household-specific estimate:
- Include a fee only when the account will actually incur it in the period being modelled.
- Apply tax at the rate and to the items covered by your jurisdiction’s rules.
- Enter a rebate or discount as a subtraction, and check its end date and eligibility.
- Show debt repayments separately from energy consumption; a repayment schedule can raise the amount due even when prices are unchanged.
- Do not treat a one-time credit as a permanent reduction in an annual budget.
If a government relief programme, VAT rate or supplier discount may change, produce a with-adjustment and without-adjustment scenario. Label the date and eligibility conditions rather than presenting one uncertain outcome as certain.
What the Great Britain price cap does—and does not—tell you
In Great Britain, Ofgem’s cap is a maximum unit rate and standing charge for covered standard variable tariffs. It does not cap the total amount a household can pay. Total cost rises with consumption, so two homes on the same capped tariff can have very different bills.
Ofgem says rates and charges can vary by region, payment method, fuel and meter type. Its described protection does not cover fixed tariffs, business contracts, heat networks or heating oil. Confirm that your tariff is within the relevant scope before using a cap table.
Ofgem’s dated Q4 2026 direct-debit average figures
For 1 October through 31 December 2026, Ofgem’s direct-debit average cap table lists the following Great Britain figures:
| Fuel | Average unit rate | Average daily standing charge | Period and scope |
|---|---|---|---|
| Electricity | 26.32 pence/kWh | 54.83 pence/day | Great Britain, direct debit, 1 October–31 December 2026 |
| Gas | 7.97 pence/kWh | 29.68 pence/day | Great Britain, direct debit, 1 October–31 December 2026 |
These are averages for that period, not guaranteed rates for an individual account. Check the current Ofgem table immediately before using the figures: region, payment method, fuel, meter type, VAT and the applicable quarter can alter the result. Ofgem notes that VAT changes can affect comparisons between periods.
Why a headline “average bill” is not your forecast
An average combines assumptions about consumption and tariff characteristics. Your bill is driven by your meter readings, rate bands, daily charges and account adjustments. Use a published average only to illustrate the scale of a change, never as a substitute for your own calculation.
Free tools Windows power users keep installed
One-click scans. No signup required.
Build scenarios instead of pretending uncertain prices are exact
Future rates, estimated readings and policy changes are uncertain. A practical budget can show several clearly labelled cases:
Rank #4
- Current-rate baseline: your latest actual or estimated usage with the rates presently in force.
- Rate-only shock: the same usage and days with the announced unit-rate and standing-charge changes.
- High-use case: the new prices with a higher kWh assumption for colder weather, extra occupants or additional appliances.
- Low-use case: the new prices with a lower kWh assumption based on planned efficiency or a milder season.
- Adjustment case: the new prices with a rebate, tax or credit included only when eligibility and timing are established.
Keep the price shock and a consumption change in separate columns. Otherwise, a colder winter can be misreported as the effect of the tariff increase.
Convert an annual result into a planning amount carefully
Dividing an annual shock by 12 gives a monthly budgeting average, not the amount that will appear on every monthly bill. Actual charges can be seasonal, and a supplier may bill on irregular meter-reading dates. Keep enough cash available for the months in which usage is highest.
Comparing tariffs or offers fairly
When the question changes from “How big is the shock?” to “Which tariff fits?” keep the comparison controlled:
- Use the same annual or bill-period kWh for every offer.
- Split electricity into the same time-of-use bands for every offer.
- Use each offer’s standing or supply charge and payment-method conditions.
- Include regional eligibility, meter requirements, fees, discounts and their expiry dates.
- Show both annual cost and the absolute difference from your current tariff.
- Consider whether your household can realistically shift usage into a cheaper period.
Australian Government guidance recommends comparing offers against actual total usage and time-of-use patterns. A tariff that looks cheap at an advertised unit rate may not be cheaper once its fixed charge, band split and account conditions are applied. No saving is assured until your own usage and eligibility have been tested.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Australia and other jurisdictions
Australian bills commonly describe a fixed supply charge and variable consumption charges, and market arrangements differ from Great Britain’s price-cap system. Use the AER’s bill definitions and the applicable state or territory rules. Australian Government energy guidance also stresses matching an offer to total usage and the household’s time-of-use pattern.
Readers elsewhere should substitute their local regulator’s rate definitions, tax treatment, meter rules and consumer protections. Do not apply a Great Britain cap, its regional assumptions or its payment-method figures to another country.
Common mistakes and how to correct them
Using the headline cap as a total-bill cap
Symptom: multiplying a published cap rate by an “average bill” and assuming your total cannot exceed it. Fix: use your own kWh and add the daily charge for every day in the period.
Quick wins for a faster PC:
Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Comparing different consumption periods
Symptom: subtracting a summer bill from a winter bill and calling the result a price increase. Fix: hold kWh and days constant when isolating price; analyse seasonal use separately.
Best Value
- It can be a gift option
- Comes with secure packaging
- Helpful in various ways
Applying one electricity rate to every kWh
Symptom: using the peak price for an Economy 7 bill. Fix: calculate each band independently from the meter’s kWh split.
Forgetting the standing charge
Symptom: calculating only unit-rate increases. Fix: multiply the old and new daily charges by the exact number of days and show that component separately.
Mixing pence and pounds
Symptom: a result 100 times too high or too low. Fix: convert pence to pounds consistently before adding totals.
Treating an estimate as a meter reading
Symptom: a precise-looking answer based on supplier-estimated kWh. Fix: label the input as estimated, use a range if useful, and update the calculation after an actual reading.
Including a discount that does not apply
Symptom: a forecast assumes a credit continues beyond its end date or eligibility period. Fix: model the credit only for the dates and account conditions that qualify.
A compact worksheet you can reuse
Set up one row per fuel and rate band:
Band | kWh | old rate | new rate | old usage cost | new usage cost
Peak electricity | ... | ... | ... | kWh × old rate | kWh × new rate
Off-peak electricity | ... | ... | ... | kWh × old rate | kWh × new rate
Gas | ... | ... | ... | kWh × old rate | kWh × new rate
Old total = old usage costs + old daily charges + old adjustments
New total = new usage costs + new daily charges + new adjustments
Shock = new total − old totalSave the bill dates, meter-reading status, tariff name, payment method, region and the date on which you obtained each rate. That audit trail lets you explain a result later and rerun it when a supplier issues a corrected bill or a new quarter’s rates.
How to use the result in your household budget
Put the estimated shock in the same period as your budget: a bill-period increase beside the relevant month, or an annual increase in a yearly plan. If your result is an annual figure, reserve a monthly average while retaining a seasonal buffer. If the result is based on estimated usage or future rates, mark it as a scenario and set a review date for the next actual meter reading or rate notice.
Outdated Drivers Are Slowing You Down
One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchPC Slower Than It Used to Be?
A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11The most decision-useful output has four lines: old cost, new cost, absolute change and percentage change. Add a note identifying the tariff, region, payment method, dates, usage source and any included credits or taxes. That is enough information for another household member—or your future self—to distinguish a real price effect from a change in consumption or billing assumptions.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
