http://arstechnica.com/business/2015/10/apple-google-microsoft-hold-more-than-336b-overseas-via-legal-tax-loopholes/

Citizens for Tax Justice (Non-profit research and advocacy group focusing on federal, state and local tax policy) concluded: "Multinational corporations’ use of tax havens allows them to avoid an estimated $90 billion in federal income taxes each year."

[Apple] would owe $59.2 billion in US taxes if these profits were not officially held offshore for tax purposes. This means that Apple has paid a miniscule 2.3 percent tax rate on its offshore profits. That confirms that Apple has been getting away with paying almost nothing in taxes on the huge amount of profits it has booked in Ireland.

Google reported operating 25 subsidiaries in tax havens in 2009, but since 2010 only discloses two, both in Ireland. During that period, it increased the amount of cash it reported offshore from $7.7 billion to $47.4 billion. An academic analysis found that as of 2012, the 23 no-longer-disclosed tax haven subsidiaries were still operating.

Microsoft reported operating 10 subsidiaries in tax havens in 2007; in 2014, it disclosed only five. During this same time period, the company increased the amount of money it held offshore from $7.5 billion to $108.3 billion, on which it says it would owe $34.5 billion in U.S. taxes. That implies that the company has paid a tax rate of just 3 percent to foreign governments on those profits, indicating that most of the cash is booked to tax havens. Microsoft ranks 3rd for the amount of cash it keeps offshore. A Wall Street Journal investigation found that over 90 percent of Microsoft "offshore" cash was actually invested by its offshore subsidiaries in U.S. assets like Treasuries, allowing for the company to benefit from the stability of the U.S. financial system without paying taxes on those profits.