A larger energy bill can reflect a longer billing period, a change in daily use, a different unit rate or a different standing charge. This tool separates those movements using figures from two bills. Its sequential breakdown helps you explain how the calculated subtotal changed and decide whether the next question belongs with the meter readings, the billing dates or the tariff applied.

Why did the energy bill change?

Separate changes in billing days, daily use and price between two bills.

Compares usage and standing charges before tax and other line items. The waterfall applies changes in a fixed order: days, daily usage, unit price, standing charge.

What the result shows

The calculation starts with the earlier bill and applies changes in a defined sequence: billing days, daily consumption, unit rate and standing-charge rate. This produces contributions that reconcile to the change between the two calculated subtotals. Because the sequence allocates the interaction between changing quantities and prices, the individual contributions should be read together rather than treated as independent measurements of causes.

Prepare the information for this review

The labels in the tool describe the measurement or record needed for each input. The following checks help keep the entered information consistent with the case you intend to review.

Earlier bill days: Enter a plain number in the unit shown, without a currency symbol or thousands separators. Keep the same measurement basis throughout the comparison and retain the source figure for checking.
Earlier bill kWh: Enter a plain number in the unit shown, without a currency symbol or thousands separators. Keep the same measurement basis throughout the comparison and retain the source figure for checking.
Earlier unit rate (p/kWh): Enter a plain number in the unit shown, without a currency symbol or thousands separators. Keep the same measurement basis throughout the comparison and retain the source figure for checking.
Earlier standing charge (p/day): Enter a plain number in the unit shown, without a currency symbol or thousands separators. Keep the same measurement basis throughout the comparison and retain the source figure for checking.
Later bill days: Enter a plain number in the unit shown, without a currency symbol or thousands separators. Keep the same measurement basis throughout the comparison and retain the source figure for checking.
Later bill kWh: Enter a plain number in the unit shown, without a currency symbol or thousands separators. Keep the same measurement basis throughout the comparison and retain the source figure for checking.
Later unit rate (p/kWh): Enter a plain number in the unit shown, without a currency symbol or thousands separators. Keep the same measurement basis throughout the comparison and retain the source figure for checking.
Later standing charge (p/day): Enter a plain number in the unit shown, without a currency symbol or thousands separators. Keep the same measurement basis throughout the comparison and retain the source figure for checking.

Check the result against the source records

Compares usage and standing charges before tax and other line items. The waterfall applies changes in a fixed order: days, daily usage, unit price, standing charge.

Start with one case whose inputs you can trace back to the original records. Run the tool and compare its labels, units and dates with that example before preparing a wider review. If a value is uncertain, record the uncertainty in your working notes and resolve it with the person who holds the source information. A neatly presented result is useful only when the assumptions behind it are also clear.

Keep a copy and agree the next action

Use Download report to keep the written result and Download results CSV when you want to work with its records in a spreadsheet. Save inputs keeps a JSON file that can be restored into this same tool later. Editing an input hides the old result until you run the tool again, which helps avoid sharing an output that belongs to an earlier set of assumptions.

Where report emailing has been configured, Email my results lets you request a copy and send the same inputs and result to this site for follow-up about your request. The form explains who receives the copy and requires a completed security check. Check the recipient address carefully before sending. The email request uses the current result, so review the entered information before choosing that option.

For help with the next step, Explore specialist support.