Why Prepaid Electricity Units Differ Each Month in South Africa: 7 Reasons

Prepaid electricity units differ each month in South Africa because the amount of electricity you receive depends on your tariff, any deductions from your payment, and—in some tariff systems—how much electricity you have already bought during the billing period. A tariff increase, accumulated service charges, a change in subsidy eligibility or an account error can also affect how many units the same amount of money buys.

However, there is an important distinction: receiving fewer units when you buy electricity is different from receiving the same units but using them faster. The first is a pricing or transaction question. The second is usually a consumption question.

There is also no single prepaid electricity price that applies to every South African household. Your supplier and tariff matter more than a neighbour’s receipt or a general claim on social media.

This guide explains how to identify what changed, check your receipts and ask your supplier for a proper breakdown.

Official sources checked on 20 September 2026. Worked examples are illustrative unless specifically identified as an official tariff example. Confirm the rates and rules applying to your meter before making a purchase decision.

First, Understand What an Electricity “Unit” Means

On a conventional prepaid electricity receipt, a unit normally means one kilowatt-hour, written as kWh.

A kilowatt-hour measures energy. For example, an appliance drawing a constant 1,000 watts, or 1 kilowatt, uses 1 kWh if it runs for one hour.

Your payment is in rand, but the electricity credited to your meter is usually expressed in kWh. These are different measurements.

If R300 buys 100 kWh, your average payment per unit is:

R300 ÷ 100 kWh = R3 per kWh.

That calculation is useful, but it does not necessarily reveal your actual energy tariff. If part of the R300 went towards a service charge or another deduction, dividing the entire payment by the units combines different costs.

For a meaningful comparison, you need to know:

• How much you paid.
• How much was allocated to electricity.
• How many paid units were issued.
• Whether any free units were included separately.
• Which tariff and deductions were applied.

Keep the full receipt rather than only the token number. A bank notification confirming that you spent R300 may not contain enough information to explain what you received.

Why Prepaid Electricity Units Differ Each Month in South Africa

1. You may be on a tariff with different pricing blocks

Some electricity tariffs charge different prices for different portions of electricity purchased or consumed during a defined period.

Under an inclining block tariff, the earlier portion is charged at a lower rate and later portions at a higher rate. A purchase that crosses a threshold can include units at more than one price.

However, do not assume every prepaid customer is on this structure.

Eskom’s 2025/26 tariff booklet records the removal of inclining block structures from its residential tariffs. This means older advice about Eskom prepaid electricity automatically becoming more expensive after a monthly threshold cannot simply be applied to later purchases. Check the tariff version covering your transaction. Eskom’s 2025/26 tariff booklet.

Municipal structures can be different. For example, Cape Town’s published 2026/27 Domestic tariff lists separate energy rates for the portions up to and above 600 kWh. That is a local tariff example, not a national rule. City of Cape Town’s electricity tariff guidance.

A fictional example of how blocks affect a purchase

Imagine a tariff with these simplified prices:

Portion purchased during the month	Illustrative price
First 100 kWh	R2 per kWh
Units above 100 kWh	R3 per kWh

Assume there are no separate charges and that these example prices already include any applicable tax.

Your first R200 purchase buys 100 kWh.

A later R200 purchase during the same period buys approximately 66.67 kWh because the first block has already been used.

The two payments are identical, but the units differ.

Now suppose your first purchase is R350:

• The first R200 buys 100 kWh.
• The remaining R150 buys 50 kWh.
• You receive 150 kWh altogether.

Your average price is approximately R2.33 per kWh, even though neither block is priced at R2.33.

That average is the result of combining two prices. It does not necessarily indicate a billing error.

2. A service charge may have been collected from your purchase

Prepaid describes how you pay. It does not automatically mean that your account has no fixed charges.

Depending on the tariff, a supplier may recover a service or network-related charge separately from the energy charge. The collection method matters: a charge may appear on a municipal account or be recovered through prepaid purchases.

Cape Town provides a current example of the latter. Its 2026/27 Domestic tariff guidance says the Services and Wires Charge is recovered through vending as a daily amount based on the days since the previous purchase. Cape Town’s explanation of residential electricity charges.

This can make one purchase look much less favourable than another.

A fictional deduction example

Suppose you make two R300 purchases on a flat energy rate of R3 per kWh:

Transaction	Payment	Other charge collected	Amount buying electricity	Paid units
Purchase A	R300	R60	R240	80 kWh
Purchase B	R300	R0	R300	100 kWh

The energy price has not changed. The amount available to buy electricity has changed.

Do not assume every lower-unit purchase is explained by a service charge. Ask for the actual deduction and the period it covers.

If a charge accumulates between purchases, buying nothing for several weeks may postpone its collection rather than remove the liability. Confirm how your particular account works before relying on stockpiled credit.

3. The tariff changed between your purchases

A price change can mean the same payment buys fewer units even when your purchasing pattern and deductions remain identical.

Use the tariff’s effective date, not the date of a news headline, to check this.

A news report may describe a proposed increase, an approved average adjustment or a bulk electricity price. None of these automatically tells you the exact retail price attached to your meter.

Eskom distinguishes tariffs for its direct customers from tariffs for municipal bulk purchases. Its official tariff information also identifies several residential tariff categories. A municipal household should therefore check its own supplier’s retail schedule rather than assume an Eskom headline percentage applies directly to its receipt. Eskom’s tariffs and charges.

How an increase changes the units

Consider a fictional flat rate rising from R2.50 to R2.75 per kWh, with no deductions:

• Before the increase, R500 buys 200 kWh.
• After the increase, R500 buys approximately 181.82 kWh.

The price rose by 10%, but the units fell by approximately 9.09%. Those percentages differ because one measures the increase in price and the other measures the decrease in quantity for a fixed payment.

This is why simply subtracting the headline increase percentage from last month’s units can produce the wrong expected answer.

4. An account deduction or adjustment reduced the electricity portion

A payment can involve more than the purchase of energy.

If your receipt shows debt recovery, an adjustment or another account deduction, ask the supplier what it represents and how it was calculated.

Do not assume such a deduction is correct merely because it appears on a receipt. Equally, do not describe every difference as a tariff increase before checking the breakdown.

Request:

• The name of the deduction.
• The account or balance it relates to.
• The rule or agreement used to calculate it.
• The amount taken from this transaction.
• The balance remaining after the deduction.
• The route for disputing an incorrect allocation.

This is particularly important if you recently moved into a property or changed account holders.

A useful question is: “How much of my payment purchased electricity, and where was the remainder allocated?”

That is more precise than asking only why electricity has become expensive.

For example, if R500 was paid but only R400 purchased energy, compare the units with the R400 electricity allocation. Separately investigate the remaining R100. Combining both questions can hide the actual cause of the difference.

5. Your tariff category or assistance status changed

Two households supplied by the same distributor can have different tariff categories.

The category attached to an account can affect energy prices, fixed charges and access to assistance. The relevant criteria depend on the supplier.

Cape Town’s residential guidance, for example, links tariff eligibility to factors including average consumption, property valuation, meter type and approved relief status. Its Lifeline tariff includes free basic electricity for qualifying customers, while its Domestic tariff does not. These are Cape Town rules and must not be applied automatically elsewhere. Cape Town’s residential tariff eligibility guidance.

If you previously received free units, check whether they were included in the transaction you are comparing.

Suppose one month’s records show:

• 100 kWh purchased.
• A separate 50 kWh assistance allocation.

You had 150 kWh available in total, but your payment bought only 100 kWh.

If the next month’s purchase produces 100 kWh without that separate allocation, the paid electricity rate may be unchanged. The issue to investigate is the missing assistance.

The 50 kWh figure here is illustrative, not a statement of universal entitlement.

Ask your municipality or supplier to confirm eligibility, collection arrangements and any renewal requirements. Do not assume a neighbour’s allocation must apply to your household.

6. You are comparing different suppliers or vending arrangements

Your friend’s R200 purchase is not a reliable benchmark unless both meters have comparable tariffs and account conditions.

A household supplied directly by Eskom, a municipal customer and a tenant using a private submeter may have different billing arrangements.

The shop, banking app or website taking your payment is also not necessarily the organisation responsible for setting your electricity tariff.

Separate these roles:

Role	What to establish
Electricity distributor	Who supplies the property and publishes the applicable tariff?
Payment channel	Which shop, bank or app processed the transaction?
Private metering operator, where applicable	Who operates the submeter and explains its charges?
Account holder	Whose account or supply agreement is associated with the meter?

If two payment channels appear to give different results, compare transactions made under the same tariff conditions. Earlier purchases, deductions and timing can make consecutive transactions different even if the payment channel has no effect on the energy price.

Where a channel displays a separate fee, record it and ask how it is charged. Avoid assuming a fee exists when the receipt does not show one.

7. There may be a meter, account or transaction error

After checking legitimate explanations, an unexplained difference deserves investigation.

Possible issues to ask the supplier to check include:

• A purchase made for the wrong meter number.
• An incorrect tariff assigned to the account.
• An unexplained or duplicate deduction.
• A receipt showing a transaction different from the one you intended.
• A replacement meter that has not been correctly associated with the account.
• A token that was issued but has not been successfully loaded.

Distinguish the units printed on the receipt from the balance displayed after entering the token.

If the receipt shows the expected units but the meter does not reflect the purchase, the problem may concern loading, meter communication or the displayed balance rather than the tariff calculation.

Record the meter number, transaction reference, purchase time and any error message. Contact the verified supplier or vending support channel.

Do not open the meter, break seals or follow unofficial instructions to bypass it. These actions will not resolve a pricing query and can create serious safety problems.

Is Prepaid Electricity Cheaper at the Beginning of the Month?

There is no universal rule that prepaid electricity is cheaper on the first day of the month.

Where a tariff uses monthly purchasing blocks, a new period can restore access to the first block. The relevant issue is the block position attached to the meter, not a special discount for shopping on a particular date.

On a flat energy tariff, with unchanged rates and no different deductions, moving a purchase from the end of one month to the beginning of the next does not by itself change the energy price.

Charges collected through purchases can further complicate the comparison. Your first purchase after a gap might include accumulated charges, even if you expected it to be the cheapest purchase.

Before changing your buying routine, ask:

1. Does my tariff have blocks?
2. What resets, and on which date?
3. Is the calculation based on purchases or measured usage?
4. Are charges recovered from my purchase?
5. Does unused credit affect anything beyond the balance on my meter?

The answers should come from the rules applying to your account.

Does Buying Small Amounts Give You More Electricity?

Splitting a purchase into smaller transactions does not automatically create extra units.

Return to the fictional tariff with the first 100 kWh at R2 and later units at R3.

A single R350 purchase gives:

• 100 kWh for R200.
• 50 kWh for R150.
• Total: 150 kWh.

If you split the same R350 into R200 and R150 purchases within the same tariff period, the result is still 150 kWh, assuming no other charges or changes.

The second purchase does not restart the cheaper block.

Smaller purchases may still help with cash flow. A household paid weekly might reasonably buy weekly. That is a budgeting benefit, not proof of a lower energy price.

Similarly, changing shops does not provide a fresh block if the tariff system tracks purchases against the same meter.

Choose a buying pattern based on your actual tariff, budget and transaction charges rather than a supposed universal trick.

Why the Same Units May Run Out Faster

If your receipt shows the same kWh as before but your balance reaches zero sooner, start by investigating consumption.

A shorter-lasting balance does not prove you received fewer units.

Consider a 2,000-watt heater running continuously at full power:

2 kW × 4 hours = 8 kWh.

Used this way for 15 days, it consumes 120 kWh. Actual use depends on the appliance’s settings, thermostat and operating pattern, but the example shows how one high-power appliance can change a household’s consumption.

Other changes to investigate include:

• Longer hot-water use.
• More people staying in the home.
• Increased cooking or tumble-dryer use.
• Heating during cold weather.
• Pumps operating for longer.
• Battery charging from the grid.
• Faulty equipment or an unexpectedly shared circuit.

You can use Eskom’s residential electricity calculator to explore appliance consumption. Treat estimates as a guide and check the assumptions.

Track usage with a simple balance calculation

For a meter displaying remaining kWh, record the balance at the same time each day.

If you add no credit during the interval:

Starting balance − ending balance = units used.

If you add a token:

Starting balance + units loaded − ending balance = units used.

For example:

• Starting balance: 80 kWh.
• Units loaded: 100 kWh.
• Ending balance: 155 kWh.

Consumption over the interval is 25 kWh.

Keep the measurement period consistent. Comparing one day’s use with a three-day interval will not reveal a meaningful trend.

How to Check Two Prepaid Electricity Receipts Properly

You can investigate a difference without an elaborate spreadsheet. Start with two complete receipts and this checklist.

Step 1: Confirm that both purchases were for the same meter

Match the meter numbers digit by digit. Do not rely only on a saved nickname in your banking app.

If the meter was replaced between purchases, note that and request confirmation of the tariff attached to the replacement.

Step 2: Record the full transaction details

Use a table like this:

Information	Earlier purchase	Later purchase
Purchase date and time
Meter number
Supplier and tariff
Total paid
Energy allocation
Other deductions
Paid units issued
Free units, if any
Earlier purchases in the same period

An empty field is a question to ask the supplier. Do not guess a missing deduction or tariff.

Step 3: Calculate the average energy price

Divide the amount allocated to energy by the paid units.

If R270 bought 90 kWh:

R270 ÷ 90 = R3 per kWh.

For a multi-block transaction, this is an average across the relevant blocks.

If you cannot separate charges from energy, label your calculation “total payment per unit”. Do not present it as the supplier’s energy rate.

Step 4: Check whether tax is already included

Compare like with like.

A rate quoted excluding VAT cannot be compared directly with a VAT-inclusive payment calculation. Look for the labels in the official schedule.

If the receipt shows a VAT component within the payment, do not subtract it and then divide by a VAT-inclusive rate. That would count the tax adjustment twice.

Step 5: Compare the full purchasing period

One top-up may be misleading. Add all purchases and paid units for the month or applicable tariff period.

Keep free allocations, refunds and reversals identifiable.

A first purchase carrying a charge and a later purchase without that charge may have very different apparent costs per unit even though the month’s transactions follow the published rules.

What to Ask When the Units Still Do Not Make Sense

Send a short, specific request through the supplier’s verified channel.

Include:

• Meter and account numbers.
• Transaction dates and references.
• Copies of both receipts.
• Amounts paid and units received.
• The discrepancy you want explained.

Then ask for the applicable tariff name, effective date, energy calculation and every deduction.

For Eskom customers, the official Eskom customer service page provides a starting point for support. Municipal customers should use their municipality or distributor’s official account-query channel.

If you rent, request the same information from the landlord or metering operator, including the tariff basis used for the submeter.

Obtain a reference number and keep the response. If the explanation only says “tariff increase”, ask for the actual before-and-after rates and calculation.

Frequently Asked Questions

How many units should R100 buy in South Africa?

There is no single answer. It depends on the tariff, applicable block, charges, deductions and any separately issued assistance.

With a fictional flat rate of R2.50 per kWh and no deductions, R100 buys 40 kWh. That is a calculation example, not a national price.

Does buying electricity at night make it cheaper?

The time you purchase a token does not automatically provide a discount.

A time-of-use tariff concerns when electricity is consumed under that tariff’s rules. It should not be confused with buying an ordinary prepaid token late at night.

Does a new month remove electricity already loaded on my meter?

A tariff-period reset and the remaining meter balance are different things. A reset of purchasing blocks does not, by itself, mean previously loaded energy disappears.

If your balance unexpectedly changes, ask the supplier to investigate the meter and account events rather than assuming it is a normal monthly reset.

Can I compare my receipt with my neighbour’s?

Yes, as a starting point, but compare supplier, tariff, meter arrangement, deductions and purchase history.

A neighbour receiving more units is a reason to ask questions, not proof that your account is wrong.

Should I buy a large amount before a price increase?

Calculate the effect under your specific tariff first. Where blocks apply, a large purchase may place more units into higher-priced portions.

Also establish whether you are buying a fixed quantity of energy or monetary credit and how the applicable system treats future tariff changes. Do not use essential household money to stockpile electricity based on an unverified saving.

Will changing my meter automatically reduce the electricity price?

Not necessarily. A meter change and a tariff change are separate matters.

Ask which tariff applies before and after the change, whether any installation costs apply, and whether your normal usage would actually cost less.

Conclusion

When prepaid electricity units differ, compare the receipts before assuming the meter is using electricity faster or that the retailer changed the price.

Identify your supplier and tariff, separate energy costs from deductions, and check whether blocks, assistance or a rate change explain the result. If the calculation still does not match, request a written breakdown tied to the exact transaction.