Energy tariff comparison

Weighted unit rate = day rate × (1 − off-peak%/100) + night rate × off-peak%/100. Tariff cost = kWh × weighted unit rate + days × standing charge. B also includes switching cost. Saving with B = A cost − B cost. Break-even kWh = (days × (B standing − A standing) + switching cost) ÷ (A weighted rate − B weighted rate), when a non-negative crossing exists. Use consumption for the exact period you want to compare and enter the same number of days for both tariffs. Split that consumption into day and off-peak use with the off-peak percentage. For a single-rate tariff, enter the same price in its day and night fields. Enter rates in full decimal currency units: a rate of 28 cents or pence is 0.28, and a daily charge of 50 cents or pence is 0.50. Add any one-off switching or exit charge to tariff B. A positive saving means B costs less for this period. The break-even figure holds the off-peak share and day count constant.

With energy used in comparison period (kwh) 3,000, off-peak share of energy use (%) 30, comparison period (days) 365, tariff a day rate (currency units/kwh) 0.28, tariff a off-peak rate (currency units/kwh) 0.28, tariff a standing charge (currency units/day) 0.5, tariff b day rate (currency units/kwh) 0.32, tariff b off-peak rate (currency units/kwh) 0.12, tariff b standing charge (currency units/day) 0.6, one-off cost of switching to b 0, the saving with tariff b for the comparison period is $23.50. Tariff A cost: $1,022.50; Tariff B cost: $999.00; Break-even consumption: 1,825 kWh; Cheaper tariff: Tariff B.

This is an estimate based on the inputs and assumptions shown on this page, not professional advice. Check anything with financial, health or safety consequences independently.

Yes. Calculations run in your browser and your numbers are not sent to a server. A share link contains the inputs you choose to share, so check it before sending it to anyone.

Yes. Pick from 33 currencies and the amounts are labelled to match. The selector does not convert between currencies, so enter prices in your own currency.

Divide it by 100 first. A unit rate of 28 cents or pence becomes 0.28 currency units per kWh. A standing charge of 50 cents or pence becomes 0.50 per day. Use the same currency for every amount.

Yes. Enter the single rate in both the day and off-peak fields for that tariff. For the other tariff, enter its separate rates and the share of your consumption that would occur during its off-peak window.

It measures the share of total kWh used during the cheaper period, not the proportion of hours that are off-peak. Use meter readings or a supplier's usage breakdown where available. The calculator applies the same entered split to both tariffs.

A higher standing charge or a switching fee can outweigh a lower weighted unit rate when consumption is low. The comparison combines all three entered costs. A negative saving with B means A is cheaper over your selected period.

There may be no non-negative usage level where the two total costs are equal. Identical weighted rates never offset different standing or switching costs. If the tariffs are identical, they cost the same at every usage level. Equality at zero usage is a separate possible result.

No. Enter rates from the offers you are considering, including applicable tax. This is a fixed-input comparison. It does not check supplier eligibility, estimate later price changes or include charges you have not entered.