How do I Value a Defined Benefit Plan

The typical way to value such payments is to think about it from an investment standpoint. Meaning, how much would I pay for an annuity (which is just a fixed series of payments) with some interest rate r that paid P dollars for n years?

The rate of return can be either a "risk-free" rate of return like you'd get from a savings account, or if you want to compare it to what you'd make investing the money yourself with a little more risk, use a higher number. 5% is a fairly conservative rate to use if you take a moderate amount of risk.

So, given that, let's say you live for 20 years after age 62. The value of that investment at age 62 would be

PV = P/r * (1- (1+r)^(-n))

or

25k/.05 * (1- (1.05^-20))  ~= 250k

But that's the value at age 62. What's the value now? To get that you'd discount that value back to the present, which means using a similar formula with n being the number of years between now and when you turn 62. Let's say that's 25 years:

PV = FV*(1+r)^(-n)

   = 250k * (1.05)^(-25) ~= 74k

That is analogous to saying if you had 74k now, you could invest it at 5% per year for 25 years, and have enough money (still earning 5%) to pay you 25k for another 20 years.

The discount rate and longevity are significant variables here. With a 10% discount rate, the present value actually drops to 39k (since you don't need to invest as much now to get to the annuity value), and if you plan to live longer than 82 the value goes up since it obviously will pay out more.