Comparing my mileage estimates to the car’s indicates 84kWh battery has a usable capacity of 75 kWh.

 

What am I doing wrong?

Probably nothing. I found the Kona dash lies as well, it's about 2% optimistic. I think it doesn't account for the 12V system load of about 0.2 kW.
So, if you sit stopped in traffic your economy doesn't drop.

To get better numbers record the energy counters read over OBD before and after. Your net energy used is: (the change in) CED - 0.98 x (the change in) CEC.
The constant accounts for battery cycle losses incurred from regen.

Your miles driven divided by that net energy used is your economy.

 

The car tracks energy used and distance driven. Pretty easy calculation for the car to handle. I don’t think they’re doing anything stupid to mislead you. Mitsubishi had that problem, led to lawsuits that were ultimately successful for vehicle owners.

I’m recording about 17.2kW/100km right now, which translates perfectly to the observed battery consumption I’m seeing

 

Comparing my mileage estimates to the car’s indicates 84kWh battery has a usable capacity of 75 kWh.

the pre-2025 Ioniq 5's had 77.4 kWh batteries which had ~ 74 kWh usable capacity (there is some buffer below 0% and above 100%).

If the 2025 Ioniq 5s with 84 kWh batteries kept the same ratio then they will have ~80 kWh usable battery.

So the calculation would be 201 miles / 0.69*80 kWh = 3.65 miles / kWh. Now there are some rounding errors and assumptions to account for here - the SOC is reported to nearest %. Is the usable battery capacity really 80 kWh (you can check by charging to 100% and using an OBD scanner)?

But you raise a good point. All of us quote miles / kWh from the dashboard without knowing how accurate this really is.

 

As with most inner workings of modern motor vehicles we don't know exactly how the software calculates things. From a practical standpoint, how accurate does a particular reading need to be? We still drive around with mostly analog gas gauges.

 

We don't know exactly how it was programmed, but you can very easily reverse engineer it with paper and pencil and compare. If you have CarScanner like tons of us do, record the energy available at the start and end of your session, same with your odometer. You can now calculate energy consumed and distance driven. I hope I don't have to explain to anybody how to use those values to calculate and compare against the car's reading.

I did this with my RAV4 a few years ago to check it's L/100km calculation using the amount of gas required to fill the tank. You know, since I'm a nerd lol It was 100% accurate.

 

In the end, it's the cost per mile that matters. Our bank accounts don't read in kWh and we don't spend kWh. I track how many kWh I put into the car and how far I drive it. Then I divide the miles by the money I spent on that electricity. So far, with about 85% of my miles being on a road trip and the rest on home charging, I'm averaging about 7.3 cents per mile.

My display read 3.3 mi/kwh after the road trip, having reset it before leaving home. I reset again upon return and now it reads 4.4 mi/kWh. But all my wallet knows is that I've spent $404 on electricity for the car as of the end of August. When I record the September numbers in a few days, I'll know more. Now that the road trip is over, that average cost per mile should decrease.

 

Yes!

As of my last charging session on 25-Sept-2025, I have driven 14806 miles in the preceding 365 days with $894.45 in charging costs resulting in $0.06/mi. That cost is higher this year than last due to our long road trips this year.

I will admit though that the charging cost calculation for our home use is a bit fuzzy though: We have net metering (NEM2) with our solar system and Time-Of-Use (TOU) billing. I estimate the kWh and cost split between home use and car charging based on the reports from Enphase (solar system), the ChargePoint Home Flex (car charging), and the bill from SDG&E. For the cabin, also on TOU billing, I estimate the split based on the SCE bill and the power report from the meter I installed on our charging plug.