Key facts
- Effective price per kWh = 60 × price per minute ÷ average billed-energy kW.
- For positive rates and matching other fees, the equal-cost average is 60 × price per minute ÷ price per kWh.
- Peak charger power is not the average over the billed interval.
- Tiered prices, connected-time billing and fixed fees need their own itemized comparison.
A per-minute EV charging tariff becomes cheaper than a per-kWh tariff only when the energy delivered during the billed time is high enough. With constant positive prices and identical other fees, the break-even average power is 60 × price per minute ÷ price per kWh. Use average power at the billed-energy measurement point, not the charger’s advertised maximum or the battery’s peak reading.
This comparison works in any currency, provided both prices use the same currency and tax basis. Every price and charging profile in the worked examples below is hypothetical. They are not current network tariffs or first-hand charging tests.
First identify what the tariff charges for
| Billing item | Calculation | What to check |
|---|---|---|
| Energy | Billed kWh × price per kWh | Which energy reading the invoice uses |
| Charging time | Billed charging minutes × price per minute | When the charging clock starts and stops |
| Connected time | Billed connection minutes × time rate | Whether noncharging minutes count |
| Session, parking or overstay charge | Apply its separate rule | Any thresholds, minimums or additional fees |
These are different billing components. ChargePoint’s official pricing guide distinguishes energy charges from time spent connected and from session or overstay charges. Its examples describe that platform’s arrangements; the precise rules for a station elsewhere depend on its operator and payment service.
Convert a flat minute price into an effective kWh price
Let E be the receipt’s billed energy in kWh and t the minutes charged under the time tariff. Define P = 60 × E ÷ t. This is the average billed-energy rate over those billed minutes. If the rate is rm per minute, then:
Time charge = rm × t.
Effective price per kWh = rm × t ÷ E = 60 × rm ÷ P.
The result is a comparison metric. It does not change a time-based invoice into an energy-based tariff. These divisions require positive energy, time and average power; compare the actual charges directly for an aborted session delivering no energy. If the clock includes time when no electricity flows, that time must remain in the calculation. Do not substitute a battery-side kW estimate for the receipt’s energy measurement.
Worked example: when 0.60 per minute beats 0.42 per kWh
Assume two compatible charging options deliver the same 30 kWh. One costs 0.60 currency units per minute; the other costs 0.42 per kWh. Assume constant rates, accurate inputs and no different taxes, session fees, parking or overstay charges.
| Average billed-energy rate | Minutes for 30 kWh | Minute-based charge | Effective price per kWh | Energy-based charge |
|---|---|---|---|---|
| 40 kW | 45 | 27.00 | 0.675 | 12.60 |
| 60 kW | 30 | 18.00 | 0.600 | 12.60 |
| 90 kW | 20 | 12.00 | 0.400 | 12.60 |
| 120 kW | 15 | 9.00 | 0.300 | 12.60 |
The equal-cost point is 60 × 0.60 ÷ 0.42 = 85.71 kW, approximately. Above that average, the minute price wins under these assumptions. Below it, the energy price wins. The threshold is an average for the billed interval, not a minimum charger nameplate rating.
Why one impressive peak does not settle the comparison
Consider another invented session: ten minutes at 150 kW followed by ten minutes at 60 kW, both measured at the billing point. The two intervals deliver 25 kWh + 10 kWh = 35 kWh. Across twenty minutes, average power is 105 kW.
At the same flat 0.60/minute rate, the charge is 12.00, or about 0.343 per kWh. Calculating with the 150 kW peak would incorrectly suggest 0.240 per kWh. At 0.42/kWh, the alternative costs 14.70.
Now suppose the time tariff instead includes five additional noncharging minutes. The same energy costs 15.00 across twenty-five billed minutes, equivalent to about 0.429 per kWh. The energy tariff becomes 0.30 cheaper. This change comes entirely from which minutes are billed.
For the vehicle and station limits behind changing charging power, see why a 350 kW charger does not always deliver 350 kW.
Different fees can change the winning tariff
The simple power threshold assumes that other charges cancel out. If the minute-based option adds a 2.00 session fee, the 30 kWh session at 90 kW costs 12.00 + 2.00 = 14.00, compared with 12.60 for the energy-only option.
For this particular purchase, solve 0.60 × (60 × 30 ÷ P) + 2.00 = 0.42 × 30. The new threshold is about 101.89 kW. A different energy purchase produces a different threshold because the fixed fee is spread across a different number of kWh.
Apply minimum bills, discounts and taxes according to the actual terms. A monthly subscription requires its own usage calculation; our charging-membership break-even guide covers that separate decision.
Check the actual network rules before using a single-rate formula
Tesla example, across supported markets: Tesla says some locations bill by energy and others by time. Its minute billing uses four power tiers. A single flat minute rate therefore cannot represent every Tesla session. Check the location and applicable tier rules in Tesla’s Supercharging support guidance.
Electrify America example, United States: its terms allow energy, charging-time, idle-time and fixed charges. Where pricing depends on a requested maximum charging rate, that rate need not be the highest power actually achieved. Its charging terms also identify the charger display as the governing price information. Do not transfer that rule automatically to another payment provider.
For a tiered tariff, calculate each billed interval under its own rule and add the charges. Keep a screenshot of the selected payment offer and the settled receipt. If the energy reading itself is confusing, use our charging-session audit and measurement-boundary guide.
A short checklist before connecting
- Confirm the billing unit and the payment route you will use.
- Check whether time means active charging, the entire connection, or a separate overstay interval.
- Use a realistic session average, with a lower-power case as well as the optimistic case.
- Include different fees, parking and tax treatment in the final comparison.
- Check rounding, minimum bills and tier changes rather than assuming a perfectly continuous flat rate.
To understand a changing session average, read how to read an EV charging curve. If the same station shows different offers, check the charging-roaming price comparison.
Frequently asked questions
Is charging per minute always worse for a slower-charging EV?
A lower average increases the effective kWh price when the minute rate stays fixed. A tiered rate, a lower base price or different extra fees can change the result.
Can I use the number printed on the charger?
Not as the session average. Use a relevant expected average before charging and billed kWh divided by billed time afterward.
What if one tariff is free?
The positive-price break-even formula no longer applies in the usual way. Compare the full payable totals directly, including any fixed, parking or overstay charges.
Source review: 12 November 2026. All numerical tariffs and charging profiles above are original illustrative calculations. This guide makes no claim that one billing method is always cheaper worldwide.
