The UAAL is an actuarial term that refers to the difference between the actuarial values of assets owned by the plan and the total benefits due to be paid. Unfunded liabilities are created when the actual plan investment returns are less than the assumed returns, and when other plan assumptions (such as years spent in retirement, larger than expected salary increases, retroactive salary increases, and pension spiking) are realized, resulting in actual costs exceeding predicted costs. Most plans amortize the unfunded amount over a set period of years, increasing the annual cost of the plan during those years, and those additional costs are typically assigned solely to the employer.