About WattWise SA
WattWise SA is a free electricity cost calculator for South African households. It answers one narrow question well: if I run this appliance for this long, at the rate on my bill, what does the electricity cost?
Last updated: 18 October 2026
Who runs this site
WattWise is an independent project run by Lance, based in South Africa. It is not a utility, a municipal service, an electricity reseller or a financial adviser. It is not affiliated with, endorsed by or operated by Eskom, NERSA or any municipality.
That independence is deliberate. Utility bills are difficult to read, tariff schedules are published as long PDFs in inconsistent formats, and most online calculators are built for other countries. The goal here is a small, accurate tool for rand-denominated rates, with a direct link to the official source document so you can confirm any figure yourself.
How the estimate is calculated
The calculator uses one standard relationship:
It then multiplies that energy figure by your energy rate in rands per kilowatt-hour. If you enter a rate in cents per kWh, it divides by 100 first. All of the arithmetic happens in your browser; nothing you type is sent to a server or stored.
What the estimate leaves out
An energy-only estimate is a deliberately limited number, and it is important to know what it does not include:
- Fixed, service, network, demand or capacity charges, which are not priced per kWh.
- Block tariffs, where the price per kWh changes as monthly use crosses a threshold.
- Time-of-use and seasonal rates, where the price depends on when electricity is used.
- VAT, levies, arrears, adjustments and other line items on the bill.
- Changes in an appliance's real draw, such as a fridge cycling or a geyser element switching off once the tank is hot.
This is why the result is described as an estimate throughout the site. It will usually differ from the total on your bill, and that difference is expected rather than an error.
How tariff links are chosen
The provider links on the calculator and in the guides point to the electricity supplier's own website, not to a third-party summary. Each link was opened and checked on the date shown next to it. Rates are not copied into the site and auto-filled, because published tariff schedules change with notice periods, and a stale built-in rate would be worse than asking you to use the rate already printed on your own bill. Where you do want the published figure, the linked schedule is the authoritative source.
If a provider link no longer reaches the right page, or a schedule has moved, that is worth reporting.
Corrections
If a calculation is wrong, a link has broken, a unit is mislabelled, or a guide states something that does not match your tariff schedule, please say so. Corrections are made to the page and the review date is updated. Substantive changes are not made silently.
Email lance5417@gmail.com with the page address and, if possible, the wording or figure that looks wrong.
Funding
The site is free to use and has no accounts or paywall. It may in future carry advertising or clearly labelled affiliate links, which are disclosed on every page where they appear and explained in the advertising and affiliate disclosure. Commercial relationships do not affect the calculator's arithmetic or the tariff figures.