Table of Contents Our pension and retiree medical and other postretirement benefits costs and liabilities are calculated using various actuarial assumptions and methodologies. We use certain assumptions including, but not limited to, the selection of the: (1) discount rate and (2) expected return on plan assets (as discussed below). These assumptions as of December 31 were: When establishing our discount rate to measure our obligations, we match high quality corporate bonds available in the marketplace whose cash flows approximate our projected benefit disbursements. Lowering the discount rate by 50 basis points as of December 31, 2020 would increase our pension and retiree medical and other postretirement benefits obligations by approximately $1.4 billion and $45 million, respectively, decrease estimated 2021 pension expense by approximately $15 million and increase estimated 2021 retiree medical and other postretirement benefits expense by less than $1 million. (1) The expected rate of return on plan assets is based upon an evaluation of our historical trends and experience, taking into account current and expected market conditions and our target asset allocation of 30% fixed income securities, 24% U.S. stocks, 22% alternative (private) investments, 16% developed international stocks and 8% emerging market stocks. The expected rate of return on plan assets component of our net periodic benefit cost is calculated based on the fair value of plan assets and our target asset allocation. Lowering the expected long-term rate of return on plan assets by 50 basis points as of December 31, 2020 would increase estimated 2021 pension expense and retiree medical and other postretirement benefits expense by approximately $70 million and $1 million, respectively. (2) During 2020, we reviewed and revised certain economic and demographic assumptions including the pension and retiree medical and other postretirement benefits discount rates and health care cost trend rates. The net effect of changing these assumptions for the pension plans resulted in an increase of $1.7 billion in the projected benefit obligation at December 31, 2020. The net effect of changing these assumptions for retiree medical and other postretirement benefits plans resulted in an increase of $80 million in the accumulated postretirement benefit obligation at December 31, 2020. We also revised our mortality assumptions to incorporate the new improvement scale issued by the Society of Actuaries. This resulted in a decrease in our pension and retiree medical and other postretirement benefit obligations by $140 million and $1 million, respectively. See Note 10 to AAG’s Consolidated Financial Statements in Part II, Item 8A and Note 8 to American’s Consolidated Financial Statements in Part II, Item 8B for additional information regarding our employee benefit plans. Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are recorded net as noncurrent deferred income taxes. Our ability to use our NOL Carryforwards depends on the amount of taxable income generated in future periods. We provide a valuation allowance for our deferred tax assets when it is more likely than not that some portion, or all of our deferred tax assets, will not be realized. We consider all available positive and negative evidence and make certain assumptions in evaluating the realizability of our deferred tax assets. Many factors are considered that impact our assessment of future profitability, including conditions which are beyond our control, such as the health of the economy, the availability and price volatility of aircraft fuel and travel demand. We presently have a $34 million valuation allowance on certain net deferred tax assets related to state NOL Carryforwards. There can be no assurance that an additional valuation allowance on our net deferred tax assets will not be required. Such valuation allowance could be material. 86 Income Taxes 2020 2019 Pension weighted average discount rate  2.7  % 3.4  % Retiree medical and other postretirement benefits weighted average discount rate  2.4  % 3.3  % Expected rate of return on plan assets  8.0  % 8.0  % (1) (1) (2)