Since launching Office 365 two years ago, we have continued to invest deeply in our infrastructure to ensure a highly available service. 

We measure availability as the number of minutes that the Office 365 service is available in a calendar month as a percentage of the total number of minutes in that month.  We call this measure of availability the uptime number.

Within this calculation we include our business, government and education services. The worldwide uptime number for Office 365 for the last four quarters beginning July 2012 and ending June 2013 has been 99.98%, 99.97%, 99.94% and 99.97% respectively. 

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