why you think you need to do the calculations is unclear except if this is a foreign pension.
could you provide more info if this is not the case.
normally
for distributions from any one account, you get 1 1099-R for the total that is shown in box 1. the taxable amount is shown in box 2a. sometimes it is left blank because the trustee doesn't know if you have tax basis which needs to be entered. form 8606 is used to report your basis and the non-taxable portion is calculated automatically based on 2 entries you make
for the 8606 your prior year tax basis is entered on line 2 and the value of all your traditional (non-Roth) IRAs, SEP's and SIMPLE's on 12/31/2022 are entered on line 6. the non taxable portion is calculated from that.
so as of today you can't calculate the nontaxable portion be 12/31 has arrived yet.
now if it's a foreign pension then I would understand because you probably get no tax reporting form
