You don't.
Your annual withdrawals from your portfolio will be your planned spending less the pension, aka the gap. And then look at your withdrawal rate (gap divided by asset value) and see if it is excessive. For those who retire early, before pensions or SS start, it isn't uncommon for early year withdrawals to be more than 4%, but what is most important is the ultimate withdrawal rate once pensions and SS start.
Have you run your situation through FIRECalc? What you will find is that the success rate (probability of not running out of money) isn't all that sensitive to asset allocation (AA). Success rates are about the same for AA's between 40/60 and 90/10. So while for that broad range of AAs the success rate is similar, what is different are the terminal values (portfolio values at the end of the time horizon) with higher stock allocations generally resulting in higher terminal values.
Retired Big 4 CPA here, and I taught Intermediate Accounting at our local community college for a few years when I was working in industry in my mid-30s and really enjoyed teaching, especially the contact time.