Our effective tax rate was 19% and 169% for the three months ended December 31, 2018 and 2017, respectively, and 16% and 98% for the six months ended December 31, 2018 and 2017, respectively. The decrease in our effective tax rate for the three and six months ended December 31, 2018 was primarily due to the net charge related to the enactment of the TCJA in the second quarter of fiscal year 2018.
Our effective tax rate for the three and six months ended December 31, 2018 was lower than the U.S. federal statutory rate, primarily due to earnings taxed at lower rates in foreign jurisdictions resulting from producing and distributing our products and services through our foreign regional operations centers in Ireland, Singapore, and Puerto Rico, and tax benefits relating to stock-based compensation.
Recent Tax Legislation
On December 22, 2017, the TCJA was enacted into law, which significantly changed existing U.S. tax law and includes numerous provisions that affect our business, such as imposing a one-time transition tax on deemed repatriation of deferred foreign income, reducing the U.S. federal statutory tax rate, and adopting a territorial tax system. In fiscal year 2018, the TCJA required us to incur a transition tax on deferred foreign income not previously subject to U.S. income tax at a rate of 15.5% for foreign cash and certain other net current assets, and 8% on the remaining income. The TCJA also reduced the U.S. federal statutory tax rate from 35% to 21% effective January 1, 2018. The TCJA includes a provision to tax GILTI of foreign subsidiaries and a base erosion anti-abuse tax (“BEAT”) measure that taxes certain payments between a U.S. corporation and its foreign subsidiaries. The GILTI and BEAT provisions of the TCJA were effective for us beginning July 1, 2018.
The TCJA was effective in the second quarter of fiscal year 2018. We recorded a provisional net charge of $13.8 billion in the second quarter of fiscal year 2018, and $13.7 billion for the fiscal year ended June 30, 2018, related to the TCJA based on reasonable estimates for those tax effects. We adjusted our provisional net charge by recording an additional tax expense of $157 million in the second quarter of fiscal year 2019, related to GILTI deferred taxes pursuant to SEC Staff Accounting Bulletin No. 118. As of December 31, 2018, the U.S. Treasury Department and the Internal Revenue Service (“IRS”) are still in the process of issuing various TCJA regulations. Accordingly, future adjustments to the financial statements may be necessary as regulations are issued and when we file our fiscal year 2018 tax returns with the IRS and foreign tax authorities in the current fiscal year.
We recorded an estimated charge of $17.8 billion in the second quarter of fiscal year 2018, and $17.9 billion in fiscal year 2018, related to the one-time transition tax on the deemed repatriation of deferred foreign income, which was included in the provision for income taxes on our consolidated income statements and income taxes on our consolidated balance sheets. To calculate the transition tax, we estimated our deferred foreign income for fiscal year 2018 because these tax returns are not complete or due. Fiscal year 2018 taxable income will be known once the respective tax returns are completed and filed. In addition, U.S. and foreign audit settlements may significantly impact the estimated transition tax. The impact of the U.S. and foreign audits on the transition tax will be known as the audits are concluded.
In addition, we recorded an estimated benefit of $4.0 billion in the second quarter of fiscal year 2018, and $4.2 billion in fiscal year 2018, from the impact of changes in the tax rate, primarily on deferred tax assets and liabilities, which was included in provision for income taxes on our consolidated income statements and deferred income taxes and long-term income taxes on our consolidated balance sheets. We remeasured our deferred taxes to reflect the reduced rate that will apply when these deferred taxes are settled or realized in future periods. We adjusted our provisional benefit by recording tax expense of $157 million in the second quarter of fiscal year 2019.
The TCJA subjects a U.S. corporation to tax on its GILTI. Under GAAP, we can make an accounting policy election to either treat taxes due on the GILTI inclusion as a current period expense or factor such amounts into our measurement of deferred taxes. We elected the deferred method, under which we record the corresponding deferred tax assets and liabilities on our consolidated balance sheets.
Uncertain Tax Positions
While we settled a portion of the IRS audit for tax years 2004 to 2006 in the third quarter of fiscal year 2011, a portion of the IRS audit for tax years 2007 to 2009 in the first quarter of fiscal year 2016, and a portion of the IRS audit for tax years 2010 to 2013 in the second quarter of fiscal year 2018, we remain under audit for those years. We continue to be subject to examination by the IRS for tax years 2014 to 2017. In February 2012, the IRS withdrew its 2011 Revenue Agents Report for tax years 2004 to 2006 and reopened the audit phase of the examination. As of December 31, 2018, the primary unresolved issue for this and other open IRS audits relates to transfer pricing. While we believe our allowances for income tax contingencies related to the unresolved issues are adequate, the final resolution of these issues, if unfavorable, could have a material impact on our consolidated financial statements. We have not received a proposed assessment for the unresolved issues and do not expect a final resolution of these issues in the next 12 months. Based on the information currently available, we do not anticipate a significant increase or decrease to our tax contingencies for these issues within the next 12 months.
We are subject to income tax in many jurisdictions outside the U.S. Our operations in certain jurisdictions remain subject to examination for tax years 1996 to 2018, some of which are currently under audit by local tax authorities. The resolution of each of these audits is not expected to be material to our consolidated financial statements.
While we believe our allowances for all income tax contingencies are adequate, the final resolution of these issues, if unfavorable, could have a material impact on our consolidated financial statements. Tax contingencies and other income tax liabilities were $15.4 billion and $15.1 billion as of December 31, 2018 and June 30, 2018, respectively, and are included in long-term income taxes on our consolidated balance sheets. This increase relates primarily to current period intercompany transactions and interest accruals.