receiving the benefit as a life annuity. The amount of the annuity benefit must be definitely determinable as per IRS regulation 1.412-1. Defined benefit plans may be either funded or unfunded. In a funded plan, contributions from the employer and participants are invested into a trust fund dedicated solely to paying benefits to retirees under a given plan. The future returns on the investments and the future benefits to be paid are not known in advance, so there is no guarantee that a given level of contributions will meet future obligations. Therefore, fund assets and liabilities are regularly reviewed by an actuary in a process known as valuation. A defined benefit plan is required to maintain adequate funding if it is to remain qualified. In an unfunded plan, no funds are set aside for the specific purpose of paying benefits. The benefits to be paid are met immediately by contributions to the plan or by general assets. Most government-run retirement plans, including Social Security, are unfunded, with benefits being paid directly out of current taxes and Social Security contributions. Most nonqualified plans are also unfunded. Hybrid and cash balance plans Hybrid plan designs combine the features of defined benefit and defined contribution plan designs. In general, they are treated as defined benefit plans for tax, accounting, and regulatory purposes. As with defined benefit plans, investment risk is largely borne by the plan sponsor. As with defined contribution designs, plan benefits are expressed in the terms of a notional account balance, and are usually paid as cash balances upon termination of employment. These features make them more portable than traditional defined benefit plans and perhaps more attractive to a highly mobile workforce. A typical hybrid design is the cash balance plan, where the employee's notional account balance grows by some defined rate of interest and annual employer contribution. In the United States, conversions from traditional plan to hybrid plan designs have been controversial. Upon conversion, plan sponsors are required to retrospectively calculate employee account balances, and if the employee's actual vested benefit under the old design is more than the account balance, the employee enters a period of wear away. During this period, the employee would be eligible to receive the already accrued benefit under the old formula, but all future benefits are accrued under the new plan design. Eventually, the accrued benefit under the new design exceeds the grandfathered amount