The Per-100-Miles Math
Fuel costs are easiest to compare per 100 miles:
- EV: ~28 kWh per 100 miles (incl. charging losses) × your electricity rate
- Gas car: 100 ÷ mpg × price per gallon
| Scenario | EV per 100 mi | Gas (30 mpg, $3.40/gal) | You save |
|---|---|---|---|
| Home off-peak ($0.10/kWh) | $2.80 | $11.30 | 75% |
| Home average ($0.16/kWh) | $4.50 | $11.30 | 60% |
| Mostly public Level 2 ($0.35/kWh) | $9.80 | $11.30 | 13% |
| Mostly DC fast charging ($0.50/kWh) | $14.00 | $11.30 | −24% (you pay more!) |
That last row is the one no car brochure shows you: an EV charged mainly at DC fast chargers can cost more than gas. Your savings live and die with your charging mix.
Why Generic Calculators Get Your Number Wrong
- They assume a national average electricity rate — yours may be half or double it.
- They assume 100% home charging — real drivers mix in public and fast charging.
- They use EPA efficiency — winter and highway driving shift real consumption by 20–40%.
- Gas prices move weekly; a January estimate is stale by June.
We've broken down what home charging really costs per kWh here: How much does it cost to charge an EV at home? And for a quick estimate with your own numbers, there's the charging cost calculator.
Measure Your Savings From Real Sessions
ChargeDoc computes the comparison from data, not assumptions:
- Capture charging automatically — home sessions via your wallbox (go-e, Wallbox Pulsar, Tesla Wall Connector), public charges added manually in seconds.
- ChargeDoc derives your true average price per kWh across home, work, and public charging.
- Open "EV vs. Gas Car": your actual cost per 100 miles side by side with a comparable gas car at current fuel prices — with your savings percentage, monthly savings, and a yearly projection.
- Share it: one tap creates a shareable image — the "my EV runs on $4.50, the gas car on $11.30" post that settles the dinner-table argument.
Turning the Number Into Strategy
Once the number is live, it becomes useful: if your savings dip, your fast-charging share crept up or your rate changed. Shift more charging into the cheap overnight window and watch the yearly projection climb. Self-employed? The same tracked sessions double as your tax documentation.
Bottom Line
With home charging you realistically save 40–60% versus gas — more with an off-peak plan, and potentially nothing at all with fast-charging-only habits. The honest answer to "how much am I saving?" isn't in a table; it's in your own charging data. ChargeDoc works it out for you automatically.