Ok, I think I understand what you are asking and will do my best to help you, but let me know if I'm not hitting on your question.
So the “R” in SIRAGE is the expected return on plan assets, not the actual. So for that component of pension expense, you take the plan assets at the beginning of the year x the expected return on assets (this is a negative number to your total pension expense). However, later on in your computation, you have to amortize gains or losses on the pension which can arise from two areas: 1) expected return greater than or less than actual return on assets or 2) change in actuarial assumptions. This is where it is important to know both your expected and actual return on plan assets. For example:
Say you are given a fact pattern that says your actual and expected returns for 2002 are the same (say, 12%), but you have a net loss on plan assets of $50,000. Well you could accurately deduce that the net loss came from a change in actuarial assumptions that increased the pension benefit obligation (because expected and actual were the same!). However, say actual return was $60,000 and expected (when calculated) yields an expected return of $54,000, this results in a gain from actual/expected differences of $6,000. Now, combined with the change in actuarial assumption that resulted in your $50,000 loss, you now have a net loss of $44,000. So far so good?
The last part is how much you are going to have to amortize…you must amortize MINIMUM the excess of the unamortized gains or losses over 10% of the GREATER of beginning plan assets or PBO, divided by the expected remaining service life of your employees (let's say, in this hypothetical scenario, 30 years). Thus, if you have the following information:
12/31/2001 12/31/2002
FV Plan Assets $100,000 $200,000
PBO $1,500,000 $1,750,000
Unamortized G/(L) ($450,000) ($484,000)*
So, in this case, to find out how much I had to amortize, I needed to calculate 10% of both beginning plan assets and pbo and see if my unamortized g/l (in this case, loss), exceeded the greater amount. 10% of the PBO was greater in this scenario at $150,000 and unamortized G/L was $450,000 at the beginning of the year. This gives us eligible amortization of $300,000 divided by remaining service life (30 years) = $10,000 of amortization this year.
*Ending balance calculated as follows: Beginning unamortized loss – amortization of loss + current year loss = ending unamortized loss. ($450,000) – $10,000 + ($44,000) = ($484,000).
I hope I didn't confuse you…this whole convoluted example was my attempt at explaining that you only need the ACTUAL return on assets in order to see if there is anything that needs to be added/subtracted from unamortized gain or loss for the year. Let me know if that makes sense…good luck!