Your electricity statement covers more kWh than last time. Before deciding that your daily routine changed, check how many days each statement covers. A longer measurement window can contain more electricity use even when the average per day stays the same.
Create My Piggy in your browser to set a manual utilities target and compare it with expenses you explicitly record. No account or app download is required. For the separate rate-only experiment below, open the electricity calculator and replace its monthly defaults with the daily inputs described here.
Prepared with AI assistance and editorial checks. All worked quantities, dates and prices below are fictional—not a utility tariff or a household's bill.
Start with the period, not the payment amount
Tucson Electric Power's undated Factors That Impact Your Electric Bill page explains that billing periods can differ in length and suggests looking at average daily use when comparing bills. We checked that guidance on October 26, 2026. It supports a comparison method, not a claim about your supplier's exact billing schedule or a Piggy endorsement.
Write down each bill's start and end dates, stated number of billing days, total kWh and whether the reading is actual or estimated. Use the utility's stated day count; do not accidentally count a boundary date twice. If a bill includes an adjustment or overlaps another period, resolve that before treating the totals as comparable.
A fictional comparison: more kWh, same daily average
For an October 26, 2026 planning example, assume period A contains 280 kWh across 28 stated billing days, while period B contains 320 kWh across 32 stated billing days. Both give 10 kWh per day: 280 ÷ 28 = 10 and 320 ÷ 32 = 10. Period B contains 40 more kWh, but these figures do not show an increase in average daily consumption.
Assume a deliberately simplified flat USD 0.25 per kWh variable charge in both periods, excluding taxes, fixed charges, discounts, credits, fees and adjustments consistently. Period A's modeled energy charge is 280 × 0.25 = USD 70.00. Period B's is 320 × 0.25 = USD 80.00. The USD 10.00 difference comes entirely from the four extra days in this example. These are energy components, not complete bills or actual savings.
The same daily average is not an explanation of every cause
Dividing by days controls one difference: the measurement window. It does not control weather, occupancy, appliance use or the timing of consumption. Two periods can have the same daily average while individual days look very different. The calculation alone cannot prove a habit change, an appliance fault or a billing error.
Keep kWh per day separate from dollars per day. A higher average daily cost can result from a different rate or other charges even when daily kWh is unchanged. A total bill divided by kWh is an all-in average, not automatically the variable price you should enter in this simplified calculator. Time-of-use, tiered and demand charges require the applicable supplier's detail.
Now isolate a hypothetical rate change
Hold consumption at the same 10 kWh per day. Compare a fictional flat variable rate of USD 0.25 with USD 0.30 per kWh, on the same basis excluding tax, fixed charges, fees, discounts and credits. The rate difference is USD 0.05 per kWh. At 10 kWh daily, that is 0.05 × 10 = USD 0.50 more per day.
In the electricity preset keep USD and kWh, set previous price to 0.25, scenario price to 0.30, units per purchase to 10, purchases per period to 1 and repeat period to Day. Here, the form's purchase labels represent one day's modeled energy quantity, not a daily payment to your utility. Leave the optional monthly target blank unless you have a relevant variable-charge target. Confirm compatibility only when the unit and charge treatment match; changing labels does not convert units or currencies.
The verified output is about USD 3.51 more per weekly equivalent, USD 15.21 more per average month and USD 182.50 more annually. The annual result assumes that same daily use and rate difference for 365 days: 0.50 × 365 = 182.50. Monthly is 182.50 ÷ 12, not a prediction of your next calendar-month bill. The preset link opens its original monthly defaults; it does not remember these replacement inputs.
Use the actual bill length for a limited-period question
If you want only the effect of that fictional rate change over 32 days, multiply USD 0.50 by 32 = USD 16.00. For 28 days it is USD 14.00. Those are separate hand calculations, not the calculator's average-month output. Do not add them to USD 15.21; they are different time windows for the same price-only question.
For the 32-day period, the old variable charge is 320 × 0.25 = USD 80.00 and the hypothetical new charge is 320 × 0.30 = USD 96.00. Their difference is USD 16.00. Fixed service charges, taxes and other bill components remain outside the model. The calculator does not import a utility bill, verify meter data or forecast usage.
Your takeaway: compare the same window before changing the plan
First compare kWh per stated billing day. Then separate the variable rate from fixed and other charges. Use your supplier's explanation if something still does not line up; this arithmetic is a starting point, not a bill audit.
Try the electricity rate-only scenario with your own compatible inputs, then review your manual utilities target. Piggy records only what you explicitly enter, not a bank feed or complete household spending. Optional saving is browser-local, not cloud backup or native-app sync; a budget target does not reserve or pay money.
Sources and coverage
The primary utility source supports checking billing days and average daily use; it does not supply the worked prices or quantities. All example figures are fictional assumptions dated October26,2026. No current supplier tariff, guaranteed savings, meter diagnosis or petroleum-inventory quantity is claimed. The calculator models one compatible variable-price difference at unchanged quantity and frequency.
A little clarity, not a guarantee
Projections are not recorded spending or confirmed savings. No national average or future price is inferred. The web calculator does not upload receipts, send family requests, or update the iPhone app.