I usually wind up configuring the calculator to include my sales tax, adjust what incentives I’m qualified for, whether I’m using MSDs, etc and then take the total lease cost and divide by the number of months to get the net effective monthly cost.
I think it’s a useful stat to compare actual lease costs and would be simple to add to the calculator.
You have to be very careful to separate common costs from direct costs. Common costs should not be considered in making baseline lease cost comparisons and include costs that everyone pays but could be different depending upon governing jurisdictions such as taxes and dmv/gov fees. Only those costs that are controlled by the lessee (credit - lease rate), fund provider (mf, acq fee), or dealer (marked-up fees) should be considered these include mf, acq fee, doc fee. None of these three entities has any control over taxes (except, perhaps, in the case of issuing tax credits) or dmv/government fees.
For example, suppose there are two deals from two different geographic areas that are exactly alike EXCEPT for taxes and, the monthly payment triggered by taxers. Area A levies tax at 4.5% and Area B 11%. One can’t argue that lessee A got the better lease deal as both lease deals are identical (excluding taxes). In other words, the only way one can make a legitimate comparison is to exclude taxes for which none of entities has little or no control.