### Understanding Home Charging Costs

Let’s start simple and assume you charge entirely at home. There are three things you need to know to calculate monthly charging costs:

1. How much you drive (an estimate, in miles)
2. How efficient your EV is (in mi/kWh, more below)
3. How much you pay for electricity (consult your bill for this)

#### How much do you drive?

The average American drives just under 13,500 miles per year, or about 1,123 miles per month. We’ll use this number for our examples, but feel free to substitute in your own monthly estimate. Make sure to factor in any longer trips or weekly errands.

#### How efficient is your EV?

There are two main measures of EV efficiency:

1. miles per kilowatt-hour (mi/kWh), and

2. watt-hours consumed per mile driven (Wh/mi)

You may also see efficiency measured in kWh/100 miles on websites like fueleconomy.gov. It's common to see a value such as 30 kWh/100 miles. If you flip and simplify this fraction, (100 ÷ 30), you get the efficiency in mi/kWh (3.33 miles / kWh).

Most car dashboards report efficiency in mi/kWh, whereas Tesla generally uses Wh/mi. If you only have your efficiency in Wh/mi, you can easily convert to mi/kWh following the example below.

In this article, we’ll be using mi/kWh.

#### What is typical efficiency?

In most mid-size electric cars, in most circumstances, efficiency is between 3-4 miles per kWh. These numbers may go up or down depending on driving habits and weather. If you drive a truck, your efficiency numbers will likely be lower. For some context, consider the extreme ends of the efficiency spectrum: some people can “hypermile” into 5+ mi/kWh territory, while the inefficient Hummer EV gets less than 2 miles per kWh. You can check the average, rated efficiency for most EVs on fueleconomy.gov.

Remember that for any EV, speed is the main thing that affects efficiency. The faster you go, the lower your efficiency. If you care about great efficiency, slow and steady is the way to go (and it may possibly save you some money).

#### How much do you pay for energy?

This is perhaps the most variable part of the equation, since it depends on your specific energy provider and electricity plan. There are over 3,300 electric utility providers in the United States and many regional price differences. You can check out your local or regional electricity averages on the Bureau of Labor Statistics website, or check your energy bill for what you actually pay.

Another confounding factor in electricity pricing is that each utility provider may offer different rate plans that will further determine how and when you pay for electricity. All utility plans may not be offered to all customers, so what you pay may not even be the same as what your neighbor pays!

One type of rate plan is tiered. For example, your first 100kWh is billed at one rate, the next 300kWh at a higher rate, and then everything else at a much higher rate. This is becoming less common across the country.

As solar and EV adoption accelerates, the energy market is shifting more toward a Time Of Use plan, which provides for cheaper energy during low-demand hours. On the other hand, with time of use rates, electricity costs significantly more during peak hours.

Many EV drivers favor time of use plans. They usually encourage overnight charging when demand is low and rates are the cheapest - plus, you can set a departure time that will be convenient and when you'll likely be home. You also don’t have to worry about overtaxing the grid with time of use charging - the cheapest electricity tends to be when demand is lowest.

Some utilities offer flat rate or discount plans for EV drivers, which may require a separate meter for your EV charging station.

Personally, I pay around 27 cents per kWh after all the fees and transmission charges are factored in.

#### The Calculation: Home Charging Costs

First, let’s figure out how much energy, in kWh, you need each month for your EV. Using our sample numbers, we divide 1,123 miles per month by an average efficiency of 3.5 miles per kilowatt-hour. This gives us 320 kWh used per month.

Then, we just multiply that by the cost of energy. For example, we will use \$0.167/kWh, the average US rate for electricity in fall 2022 (since that's when we made this illustration!

Our average US EV costs \$53.44 per month to drive. As a comparison, the average gas price today is \$3.74, meaning the same mileage in a 30-mpg gas car costs almost \$140.

Let’s take the same average 320 kWh a month and see what the monthly costs are for different energy rates.

Electricity cost per kWh
• \$0.10
• \$0.20
• \$0.30
• \$0.40
1123 miles at 3.5 mi/kWh
• \$32
• \$64
• \$96
• \$128
Savings over gas car example
• \$108
• \$76
• \$44
• \$12

What about if you drive significantly more or less than the average American? Curious how you can figure out your monthly charging costs?

The basic formula for any car is:

1. Divide monthly mileage by efficiency in miles per kWh
2. Multiply the answer from step 1 by the cost of energy per kWh

Here's one more example to help you through it: my driving, my car, and my rate plan.

I drive around 800 miles a month in a car that gets 3 miles per kWh. My electricity rate is 27 cents per kWh (which is quite a bit more than the national average).

1. Divide 800 miles by 3 miles per kWh to get 26.67 kWh a month:
1. Multiply that by \$0.27/kWh:

You can see that my monthly charging cost is around \$72

For fun, let's compare my Tesla Model Y Performance to a similarly sized gas car, like a Toyota RAV4. The RAV4 averages about 30 miles per gallon. Using the same 800 miles per month, and a local gas rate of \$4.94 per gallon, it would cost me about \$132 per month to fuel a RAV4. Nearly double.

I should point out that I have very expensive electricity. Almost anywhere else in the country, charging an EV may be one-third to one-quarter the cost of driving a gas car.

### Understanding DC Fast Charging Costs

If you’re thinking about total EV charging, you need to consider DC Fast Charging (DCFC), which is a faster way to recharge an electric car when you're on the go. Fast charging is convenient, but it can be quite expensive! The cost of DC Fast Charging, which may be priced by kWh or by minute, can be about the same price as filling up a car with gas. A nice perk of many new EVs is introductory or limited free fast charging. For instance, Ford is offering 250 kWh of free charging at Electrify America stations.

The other reason that EV drivers don’t typically rely solely on DC fast charging is because it is not ideal for long term battery health. DC charging uses high voltages and produces a lot of heat - both of which can, over time, accelerate battery degradation.

Until you have fast charged an EV a few times, understanding how long it may take can be tricky. All cars come with a maximum rated DC charge speed, but most only hit that max charge rate for a small chunk of time. Batteries will recharge fastest when they are at low state of charge recharge, and typically slow down a lot once you hit 80%. It’s usually faster and safer for your battery to “top off” at a Level 2/ AC charger once you hit the 80% mark.

#### So how much does fast charging cost?

Let’s take a car with a 80 kWh battery and consider charging from 20% to 80% SoC. This means you're adding 60 percentage points of charge, or around 48kWh (0.6 x 80 kWh).

A ballpark national average for DCFC charging costs is 35 cents per kWh, with potential session fees. At 35 cents per kWh and a sample \$3.50 session charge, you would expect to pay \$20.30 for a typical road trip stop.

Charging from 0-100% at the same station would cost \$31.50 (and would take a lot longer). Again, rates vary based on region, provider, and sometimes even surge pricing. Lastly - heads up for idle fees at public charging stations. If you leave your car plugged in when it's no longer charging, you may be hit with fees for hogging the charger. Learn good etiquette and be kind to your fellow electric car drivers!

While DC fast charging can be an expensive proposition and best saved for road trips, most EV drivers are able to rely on inexpensive home charging for the majority of their needs. Not only does this make the best financial sense, but it's better for your battery, too.

Curious what it's like to drive an EV in an apartment? It's tricky, but might be do-able.