Spouse has a single traditional IRA account into which was made a non-deductible contribution one year (and the appropriate form filed with our taxes). We understand the pro rata rule for partial distributions which could be a nuisance to track in later years, but if we were to convert the full IRA this year is it a simple matter of just paying tax on the difference between the IRA total (consisting of deductible contributions and earnings) less the non-deductible contribution? I know there are other considerations to Roth conversions, but this is the first time we're doing a conversion and just want to be sure of not overlooking some possibly obscure rule related to this specific issue. Thanks.
Yes, that is correct. The taxable amount will be the amount of the conversion minus the amount of non-deductible contributions (the basis in the Traditional IRA). In the year of the conversion, since you converted all of your Traditional IRAs, you will fill out Form 8606 Part II:
16. the amount of the conversion 17. the amount of nondeductible contributions 18. the amount of the conversion - the amount of nondeductible contributions
You include line 18 as the taxable amount from the conversion on your Form 1040.