If you charge an electric vehicle (EV) at home, your electricity tariff can make a huge difference to how much you actually pay each month.
Many utilities now offer night tariffs (also called time-of-use or off-peak tariffs) that are cheaper during certain hours, while traditional flat-rate tariffs charge the same price for every kWh, 24/7.
So which one is better for EV owners?
The honest answer is: it depends on when and how you charge. In this guide, we’ll break down:
- How night tariffs and flat rates work
- Why EV charging changes the equation compared to a normal household
- Simple formulas to compare tariffs
- Real-world scenarios showing when each option wins
- A step-by-step checklist to choose the best plan for your situation
1. Flat rate vs night tariff: what’s the difference?
1.1 Flat-rate tariffs
A flat-rate tariff is simple:
- You pay the same price per kWh at all times of day
- Your bill is mostly
Energy used × price per kWh + fixed fees - Easy to understand, easy to predict
Flat rates work well for households that:
- Use energy evenly throughout the day
- Don’t want to think about when they run appliances
- Have relatively low total usage and no large flexible loads like EVs or heat pumps
1.2 Night or time-of-use (TOU) tariffs
A night tariff or time-of-use tariff has:
- Cheaper off-peak periods (often at night, sometimes weekends)
- More expensive peak periods (evenings or daytime when demand is high)
Your bill depends not only on how much you use, but also when you use it.
For example, a simple TOU plan might look like:
- Peak (7 am – 11 pm): 0.30 USD / kWh
- Off-peak (11 pm – 7 am): 0.15 USD / kWh
Some plans include additional features:
- Super off-peak windows (e.g. 1 am – 4 am at an even lower price)
- Seasonal variations (different prices in winter vs summer)
- Higher fixed monthly fees than the flat-rate alternative
For a typical household without an EV, these tariffs only make sense if you can shift washing machines, dryers, dishwashers, water heating and other big loads to off-peak hours.
But once you own an EV, you suddenly have a large, flexible load that can be moved almost entirely to night hours. That’s where night tariffs can become very attractive.
2. Why EV owners are different from “normal” households
Without an EV, your electricity usage might be:
- Roughly even across the day, or
- Heaviest in the evening when you cook, watch TV, and use lights
But with an EV:
- A big part of your consumption comes from charging
- Charging does not care what time it happens, as long as the car is ready when you need it
- Modern EVs and wallboxes allow automatic scheduling
This means:
As an EV owner, you can often move most of your new energy consumption into the cheapest hours without changing your lifestyle.
That’s very different from trying to move family showers or cooking to 2 am.
3. The simple math: how to compare tariffs
To compare tariffs, you need to estimate:
- Your total household usage without the EV
- Your EV energy usage per month or per year
- The share of EV charging you can realistically place in off-peak hours
Then you can calculate the effective average price per kWh for each tariff.
3.1 Step 1: estimate your EV energy usage
From your EV’s consumption:
EV kWh / 100 km × distance per month / 100
Example
- EV consumption: 18 kWh / 100 km
- Distance: 1 200 km / month
EV energy used:
18 × (1 200 ÷ 100) = 18 × 12 = 216 kWh / month
3.2 Step 2: estimate your household’s non-EV usage
Check old bills from before you had the EV (or before you charged at home). Suppose:
- Household usage without EV: 250 kWh / month
Total current usage with EV would be about:
250 + 216 = 466 kWh / month
3.3 Step 3: calculate cost under a flat rate
If the flat rate is 0.22 USD / kWh:
Total cost = 466 × 0.22 = 102.52 USD / month
(ignoring fixed fees, which we will compare later)
3.4 Step 4: calculate cost under a night tariff
Now assume a TOU plan:
- Peak: 0.30 USD / kWh
- Off-peak: 0.12 USD / kWh
We must estimate how much energy falls into each band.
Household energy
Let’s assume you can only move 20% of your normal household usage to off-peak hours (dishwasher, washing machine, some water heating):
- Peak household usage: 80% of 250 = 200 kWh
- Off-peak household usage: 20% of 250 = 50 kWh
EV energy
If you set your car to charge only at night, you might reach:
- Peak EV usage: 0 kWh
- Off-peak EV usage: 216 kWh
Total across the month
- Peak total: 200 kWh
- Off-peak total: 50 + 216 = 266 kWh
Now calculate cost:
Peak cost = 200 × 0.30 = 60 USD
Off-peak cost = 266 × 0.12 = 31.92 USD
Total energy cost under TOU:
60 + 31.92 = 91.92 USD / month
Compared with flat rate 102.52 USD, you save about 10.6% on energy.
If the TOU plan has higher fixed fees, subtract those from the savings to see if it’s still worth it. For example, if the TOU plan costs 5 USD more per month in fixed fees, your net savings would be:
102.52 − 91.92 − 5 ≈ 5.60 USD / month
Not huge, but still positive. For higher mileage or bigger price differences between peak and off-peak, the savings grow quickly.
4. Scenario 1: Commuter with moderate mileage
Let’s build a realistic scenario and compare flat vs night tariff step by step.
Assumptions
- EV distance: 15 000 km / year (~1 250 km / month)
- EV consumption: 17 kWh / 100 km
- Household non-EV use: 250 kWh / month
Tariff A – flat rate
- Energy price: 0.22 USD / kWh
- Fixed fee: 10 USD / month
Tariff B – night tariff
- Peak: 0.30 USD / kWh (7 am–11 pm)
- Off-peak: 0.10 USD / kWh (11 pm–7 am)
- Fixed fee: 14 USD / month
4.1 Energy usage
EV energy:
17 × (1 250 ÷ 100) = 212.5 kWh / month
Household usage: 250 kWh / month
Total: ~ 463 kWh / month
4.2 Cost under flat rate (Tariff A)
Energy:
463 × 0.22 ≈ 101.86 USD / month
Total bill:
101.86 + 10 = 111.86 USD / month
4.3 Cost under night tariff (Tariff B)
Assume:
- Household: 25% off-peak (washing machine, dishwasher, some heating)
- EV: 95% off-peak, 5% peak (a few unscheduled daytime top-ups)
Household:
- Peak: 75% × 250 = 187.5 kWh
- Off-peak: 62.5 kWh
EV:
- Peak: 5% × 212.5 = 10.6 kWh
- Off-peak: ~201.9 kWh
Peak total:
187.5 + 10.6 ≈ 198.1 kWh
Off-peak total:
62.5 + 201.9 ≈ 264.4 kWh
Peak cost:
198.1 × 0.30 ≈ 59.43 USD
Off-peak cost:
264.4 × 0.10 ≈ 26.44 USD
Energy total: 85.87 USD / month
Add fixed fee: 85.87 + 14 = 99.87 USD / month
4.4 Result
- Flat rate: 111.86 USD / month
- Night tariff: 99.87 USD / month
Savings: 11.99 USD / month, or about 143 USD per year.
For a single tariff change and a one-time scheduling setup in your car, that’s a very solid saving.
5. Scenario 2: Low-mileage driver
What if you don’t drive much? Night tariffs still sound attractive, but they may not pay off if:
- Your EV usage is low
- Your household usage is small
- The night plan has significantly higher fixed fees
Assumptions
- EV distance: 6 000 km / year (~500 km / month)
- EV consumption: 16 kWh / 100 km → 80 kWh / month
- Household non-EV use: 180 kWh / month
Tariffs similar to before, but with fixed fee difference:
- Flat rate: 0.22 USD / kWh, 8 USD fixed
- Night tariff: peak 0.30, off-peak 0.10, 15 USD fixed
5.1 Flat rate
Total usage: 180 + 80 = 260 kWh
Energy cost:
260 × 0.22 = 57.20 USD
Total bill:
57.20 + 8 = 65.20 USD
5.2 Night tariff
Assume:
- Household: 20% off-peak
- EV: 90% off-peak
Household:
- Peak: 80% × 180 = 144 kWh
- Off-peak: 36 kWh
EV:
- Peak: 10% × 80 = 8 kWh
- Off-peak: 72 kWh
Peak total: 144 + 8 = 152 kWh
Off-peak total: 36 + 72 = 108 kWh
Peak cost:
152 × 0.30 = 45.60 USD
Off-peak cost:
108 × 0.10 = 10.80 USD
Energy total: 56.40 USD
Add fixed fee: 56.40 + 15 = 71.40 USD
5.3 Result
- Flat rate: 65.20 USD
- Night tariff: 71.40 USD
Even though night energy is cheaper, the higher fixed fee and low overall usage mean the night tariff is more expensive for this low-mileage EV owner.
This is a key point:
Night tariffs are not automatically better for every EV driver. They shine when your usage is high enough and you can move most of it to off-peak.
6. Scenario 3: High-mileage driver with solar panels
Now let’s look at someone who:
- Drives a lot
- Has roof-top solar
- Can move most charging to sunny hours or cheap nights
Assumptions
- EV distance: 25 000 km / year (~2 083 km / month)
- EV consumption: 18 kWh / 100 km → 375 kWh / month
- Household non-EV use: 300 kWh / month
Solar production:
- 400 kWh / month on average
- 60% can be used directly in the home or car, the rest exported
Tariffs:
- Flat rate: 0.22 USD / kWh, 10 USD fixed
- Night tariff:
- Peak: 0.30 USD / kWh
- Off-peak: 0.12 USD / kWh
- Export price for solar: 0.06 USD / kWh
- Fixed: 14 USD
6.1 How solar changes things
Every kWh of solar energy you use yourself instead of buying from the grid:
- Saves you the retail price you would have paid
Every kWh you don’t use and export:
- Only earns the export price (often much lower)
So from a cost perspective, it’s best to:
- Charge the EV directly from solar during the day when possible
- Use night off-peak hours for any remaining energy needed
6.2 Simplified monthly picture
Let’s say:
- Of 400 kWh solar produced, 60% (240 kWh) is used directly in the house and for daytime EV charging
- The remaining 160 kWh is exported at 0.06 USD / kWh
You might use solar like this:
- 140 kWh into the EV (daytime charging)
- 100 kWh into household appliances
- 160 kWh exported
EV still needs: 375 − 140 = 235 kWh from the grid
On the flat tariff, we don’t care about time. On the night tariff, we try to pull most of that 235 kWh during off-peak.
We won’t do every step in detail here, but the key idea is:
- Solar reduces your grid usage under both tariffs
- The night tariff still helps because you can place most remaining EV charging in cheap hours
In practice, high-mileage drivers with solar often find that:
- Night tariffs + intelligent scheduling + daytime solar charging
- → give them very low effective cost per kWh for EV charging
- Sometimes below 0.05–0.08 USD / kWh equivalent
7. Non-price factors to consider
Price is important, but there are a few other aspects to think about when choosing between night tariffs and flat rates.
7.1 Complexity and effort
Night tariffs usually require:
- Setting up charging schedules in your car or charger
- Maybe moving some appliance usage to off-peak hours
- Occasionally thinking about whether to plug in now or later
If you:
- Really dislike dealing with schedules or
- Have an irregular lifestyle and departure times
you might prefer the simplicity of a flat rate, even if it’s slightly more expensive.
7.2 Reliability of cheap hours
Some plans have:
- Time slots that change by season
- Rules that your provider can modify with limited notice
If you choose such a plan, it’s worth subscribing to:
- Email notifications
- Provider apps that update tariffs automatically
So you don’t accidentally move heavy loads into a now-expensive window.
7.3 Future flexibility
Ask yourself:
- Will your driving pattern change soon?
- Are you planning a second EV, a heat pump, or more electric appliances?
If you expect electric usage to grow, a night tariff that is only marginally beneficial now may become very profitable in a year or two.
8. How to decide: a simple checklist
Here is a quick decision process you can follow:
- Collect data
- Your flat-rate price and fixed fee
- Night tariff peak/off-peak prices and fixed fee
- Your household usage from old bills (without EV if possible)
- Your EV consumption and annual mileage
- Estimate EV energy usage
- Use kWh / 100 km × distance per year, then divide by 12 for monthly
- Estimate off-peak share
- How much of your EV charging can you realistically place at night? (60–100% for most people)
- How much household usage can you move? (often 10–30%)
- Calculate monthly cost for each tariff
- Use approximate formulas like the ones earlier in this guide
- Remember to include fixed fees
- Compare and test sensitivity
- What if your mileage increases?
- What if off-peak prices change slightly?
- Decide and set schedules
- If the night tariff clearly saves money, switch and set up automatic charging
- If the difference is very small, you might stay with the flat rate for simplicity
9. Key takeaways
- Flat-rate tariffs are simple and predictable. They can still be a good choice for low-mileage EV drivers or those who value simplicity.
- Night tariffs / time-of-use tariffs can significantly reduce EV charging costs when:
- The price gap between peak and off-peak is large
- You can move most EV charging to off-peak hours
- Your total electricity usage (household + EV) is moderately high or above
- EV owners are in a unique position because charging is a flexible, schedulable load. This makes night tariffs much more attractive than for a typical household.
- Always factor in fixed fees and your realistic off-peak usage share when comparing tariffs.
- For many medium and high-mileage EV owners, a well-chosen night tariff plus automatic charging schedules can save hundreds of dollars per year with almost no extra effort.
Once you’ve chosen the right tariff, the next step is to estimate your new cost per kWh and plug it into an EV charging cost calculator. That will show you exactly how much you’re paying per 100 km and how your savings compare to a gasoline car—and that’s when the benefits of smart charging really become visible.