Eskom Tariff Calculator

How your electricity bill is built up

If you have ever bought R200 of prepaid electricity at the start of the month and felt it bought far more units than the same R200 bought near month-end, you have run into the inclining block tariff (IBT). South African residential electricity is not charged at one flat rate per kilowatt-hour (kWh). Instead, your monthly consumption is sliced into bands, and each band is priced higher than the one before it. This calculator models that banded pricing so you can see, before you buy, roughly where your usage lands and what it will cost.

What a kWh actually is

A kilowatt-hour is the unit you are billed in: one kilowatt of power drawn for one hour. A 2 000 W kettle running for 30 minutes uses 1 kWh. A 150 W fridge running all day uses roughly 3.6 kWh. Geysers are the big one in most homes, often 1 500 to 3 000 W, and an hour of heating can swallow 2 to 3 kWh. Knowing this is why the calculator asks for your monthly total in kWh rather than rands: rands change with every tariff increase, but the physical units your appliances draw stay the same.

How the blocks add up

On a Homepower-style residential tariff there are two consumption blocks. Everything up to a threshold (this calculator uses 600 kWh as the block boundary) is charged at the cheaper Block 1 rate. Every unit above that threshold is charged at the more expensive Block 2 rate. Crucially, you do not lose the cheap rate once you cross over: the first 600 kWh is always charged at Block 1, and only the excess is charged at Block 2. The total is then built up like this:

Block 1 cost = min(usage, 600) x Block-1 rate
Block 2 cost = max(usage - 600, 0) x Block-2 rate
Total bill   = Block 1 cost + Block 2 cost + fixed network charge

The fixed network charge (sometimes called a service or capacity charge) is a flat monthly amount you pay regardless of how little you use. It is why a near-empty holiday home can still receive a bill. Prepaid tariffs often fold this charge into a higher per-kWh rate instead of billing it separately, which is one reason prepaid and postpaid totals differ even at the same consumption.

A worked example

Imagine a household uses 800 kWh in a month on a tariff with a Block 1 rate of R2.50/kWh, a Block 2 rate of R3.80/kWh, and a R200 network charge. The first 600 kWh sits in Block 1 and the remaining 200 kWh spills into Block 2:

Block 1: 600 kWh x R2.50 = R1 500.00
Block 2: 200 kWh x R3.80 = R  760.00
Network charge           = R  200.00
-----------------------------------
Total                    = R2 460.00

The average works out to about R3.08 per kWh even though the headline Block 1 rate is only R2.50. That gap is the IBT at work, and it is exactly why high-consumption households feel a sharper sting than the advertised tariff suggests. Shaving usage below the 600 kWh boundary removes the expensive Block 2 portion entirely.

Prepaid versus postpaid

• Prepaid (Homepower 2 style): you buy units up front via a token. There is usually no separate monthly network charge, but the per-kWh rates tend to be a little higher to compensate. Your blocks reset at the start of each calendar month, so units bought cheap early carry over but the block counter does not.
• Postpaid / credit: you are billed in arrears and almost always carry a fixed network charge. This can be cheaper per unit for heavy users but adds a baseline cost every month.
• Lifeline / low-usage tariffs: designed for small households, these offer a low Block 1 rate but a steep Block 2 rate to discourage high consumption, so they only pay off if you stay genuinely frugal.

Using the result wisely

Treat the figure this tool gives you as a planning estimate, not an invoice. Tariffs are set annually by NERSA and differ enormously between Eskom direct-supply customers and the hundreds of municipalities that buy bulk from Eskom and resell it with their own markups, free-basic-electricity allowances, and time-of-use options. The rates built into this calculator are illustrative. Before you commit to a budget or a solar decision, confirm the current block rates, thresholds, and network charges printed on your own municipal bill or on your municipality's tariff schedule. Once you know your real rates, the arithmetic above is exactly how your true cost is assembled.