How it works
Here's the short version of how this calculator arrives at the numbers it shows you. No jargon required.
The basic idea
Electricity is sold by the - one kWh is roughly what a 1,000-watt appliance uses if you leave it on for an hour. Your power bill is mostly just:
how much electricity you used × the price per kWh in your area × how many days in the month.
For each appliance you tick, we estimate how much electricity it uses in a typical month based on its wattage and the hours you set. Add it all up, add the daily fixed charge, and that's the monthly bill.
Where the prices come from
The regional figures are from 's . It's updated every three months (February, May, August and November) and covers 42 locations across New Zealand. We refresh the data within a week of each release.
The MBIE figure is a - it models a small household on the cheapest plan available in your area and rolls the daily into the per-kWh price. That's good enough for a quick estimate. If you want to match your actual bill exactly, tap "Enter actual rates" and type the c/kWh and daily charge from your invoice.
Heat pumps are a special case
A heat pump doesn't just turn electricity into heat - it moves heat from outside to inside, so you get more heat out than electricity in. A well-tuned NZ heat pump produces around 3-4 kW of heat for every 1 kW of power it draws.
We ask for the heat output shown on the sticker (a "2.5 kW heat pump" means 2.5 kW of heat) and use a sensible default for your climate zone:
- Northern (Auckland, Northland, Waikato, Bay of Plenty): roughly 4×.
- Central (Wellington, Nelson, Marlborough): roughly 3.8×.
- Canterbury & West Coast: roughly 3.7×.
- Southern (Otago, Southland): roughly 3.3×, because cold mornings knock efficiency down.
These are averages. Your specific unit might do better or worse - you can edit the number on each heat pump row if you know yours.
Day rate vs night rate
If you're on a plan, your power is cheaper at night. Hot water cylinders are the main appliance that benefits - most NZ cylinders heat overnight on . We bill the cylinder at the night rate by default; untick the "night rate" toggle on the cylinder row if yours runs on demand.
Free hours and free power days
Some retailers throw in a every day (Electric Kiwi's Hour of Power is the classic example). Others give you a once a month (Mercury). You can enter both in the advanced rates panel and the calculator credits you back accordingly. The credit is capped at your bill, so you can't push it below zero.
Winter vs summer
Your monthly total shows what a steady month would cost if you used your appliances the same way every day. But heaters don't run in January and air conditioners don't run in July, so the annual figure weighs each month realistically - heating costs more in winter, cooling in summer. Everything else (fridge, lights, laundry) is assumed to run year-round.
Looking at old prices
The quarterly pricing data goes back to 2004. Click the period dropdown to see what rates looked like in any given quarter since then. It only swaps the price - your appliance list stays the same - so you can answer "what would today's usage have cost me in 2010?"
Where this calculator keeps it simple
- Spot-price retailers. Flick and similar retailers change the rate every half hour. We assume a flat rate.
- Peak-window surcharges. Some retailers charge more during the 5-9pm peak. If yours does, nudge the day rate up by a cent or two.
- Solar and batteries. Rooftop solar has its own payback calculator. If you have panels or a battery, that page is what you want for those numbers.
- GST. All figures include it, to match how retailers show prices.
Does the number look wrong?
Email [email protected] with what you entered and what you expected. Actual bills with real retailers are the most useful kind of feedback - they're how we validate the numbers are landing in the right ballpark.