Do not assume a 200-amp heavy-up “covers the ADU too.” An accessory dwelling unit has cooking, water heating, HVAC, and lighting of its own. Codes and local amendments treat that as additional dwelling load, sometimes in a separate panel fed from the same service, sometimes as a new service. A Level 2 charger on the main house, plus an ADU, plus a heat pump, is exactly the stack that makes people ask about 320- or 400-amp or dual 200-amp arrangements — see that page. A 200-amp service may still be enough if the ADU is small, all-gas, or on listed energy management, but that is a calculated result.
This site will not invent a typical ADU ampere number. What you can do now is put the house and the planned ADU on one planning sheet: floor area, range, water heat, HVAC, and the charger setting, then have an electrician run the method the local department uses for a two-dwelling property. The optional-method walk-throughs on the 200-amp combination pages (for example about 131.4 A in the heavier single-house example) do not include a second dwelling and should not be stretched to cover one.
If the ADU is years away, say so in the upgrade quote so the meter, the trough, and the panel location are not built into a corner. Use the calculator for the house-plus-charger piece, and treat the ADU as a separate, documented add.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.