Actuarial Assumptions: Discount Rate :
The rate used to discount post-employment benefit obligations (both funded and unfunded) should be determined by reference to market yields at the balance sheet date on government bonds. The currency and term of the government bonds should be consistent with the currency and estimated term of the post-employment benefit obligations.
One actuarial assumption which has a material effect is the discount rate. The discount rate reflects the time value of money but not the actuarial or investment risk. Furthermore, the discount rate does not reflect the enterprise-specific credit risk borne by the enterprise’s creditors, nor does it reflect the risk that future experience may differ from actuarial assumptions
The discount rate reflects the estimated timing of benefit payments. In practice, an enterprise often achieves this by applying a single weighted average discount rate that reflects the estimated timing and amount of benefit payments and the currency in which the benefits are to be paid.
In some cases, there may be no government bonds with a sufficiently long maturity to match the estimated maturity of all the benefit payments. In such cases, an enterprise uses current market rates of the appropriate term to discount shorter term payments, and estimates the discount rate for longer maturities by extrapolating current market rates along the yield curve. The total present value of a defined benefit obligation is unlikely to be particularly sensitive to the discount rate applied to the portion of benefits that is payable beyond the final maturity of the available government bonds.
Interest cost is computed by multiplying the discount rate as determined at the start of the period by the present value of the defined benefit obligation throughout that period, taking account of any material changes in the obligation. The present value of the obligation will differ from the liability recognised in the balance sheet because the liability is recognised after deducting the fair value of any plan assets and because some past service cost are not recognised immediately. [Illustration I attached to the Standard illustrates the computation of interest cost, among other things]