60 seconds * 60 minutes * 24 hours * 365 days = 31536000 99.99999% of that is (0.9999999 * 31536000) = 31535996.8464 31536000 - 3153996.8464 = 3.1536 seconds Or the quicker way: (60*60*24*365 * 0.0000001 = 3.1536) 99.99999% uptime = 3 seconds downtime per year 99.9999% uptime = 31 seconds downtime per year 99.999% uptime = 5 minutes downtime per year 99.99% uptime = 52 minutes downtime per year 99.9% uptime = 8 hours downtime per year