Peak and Off-Peak Usage Split Calculator

Who this is for

Whether your two-rate tariff is paying off. Read the day and night registers on your meter and the sheet works out the kWh used in each, what they cost at your peak and off-peak rates and what the same use would cost at a single rate you want to compare. The summary shows your off-peak share and the net saving or loss.

Homes on Economy 7, Economy 10 or another time-of-use electricity tariff, especially those with storage heaters or a hot water cylinder, who want to know whether the cheaper hours are being used enough.

What this helps you track

• Day and night register readings with their dates
• kWh used at peak and off-peak rates between readings
• What each period cost at your two rates
• What the same use would cost at a single rate you choose
• Your off-peak share and the net saving or loss

How to use it

1. Write your peak rate, off-peak rate and the single rate you want to compare against, all in pounds per kWh, with the off-peak hours your tariff uses.
2. Read both registers on the same day, noting which is day and which is night from your meter or supplier, and write them on a new line.
3. Read them again weekly or monthly, on the same day each time.
4. The kWh, costs and single-rate comparison are worked out in the browser and the workbook; on paper, take each reading from the one above.
5. After a few months, check the off-peak share and net saving in the summary, and move timed loads into the cheap hours if the figures are close.

Formats

• Printable PDF (A4 and US Letter)
• Fillable PDF with form fields
• Fill in online, saved in your browser
• Excel / Google Sheets workbook

The printable is laid out inside a box that fits both A4 and US Letter, so the two files are identical and neither one is scaled. The fillable PDF has real form fields. The workbook uses plain formulas only — SUM, IF, COUNTIF and the like — so it opens in Excel, LibreOffice and Google Sheets without anything breaking, and every calculated cell is grey so you can see which figures it worked out.

How to print

Download the A4 or US Letter file to match the paper in your printer, open it in a PDF reader and print at 100% — not "fit to page", which shrinks the writing space. Both files leave a 14 mm margin, which clears the unprintable edge on home printers. To print the online version with your entries in it, use the Print this sheet button, which prints only the sheet and none of the page around it. More on printing.

Questions

Which register is day and which is night?

Meters label them differently, and some show them as rate 1 and rate 2. Check with your supplier or the meter's display which is off-peak, and write it in the notes so the readings always go in the right column.

Where does the single rate come from?

From a real quote or tariff you could switch to, or from the energy tariff comparison spreadsheet. The sheet does not suggest one; it prices your own use at whatever single rate you enter.

Are standing charges included?

No, only unit costs. If the single-rate tariff has a different standing charge, compare that separately with the standing charge and annual cost projection calculator, and add the difference to the result here.

What does a negative difference mean?

The difference is the single-rate cost minus the two-rate cost. A plus figure means the two-rate tariff saved money in that period; a minus figure means a single rate would have been cheaper for that use.