Some web host offer 99.99% uptime. Is it realistic to get 99.99% uptime?

Probably this is not possible.

If we look at these percentages and convert them into the amount of time your site is going to be down we get some very telling information.

99% – 5256 Min/Yr or 87.6 Hours/Yr – 438 Min/Month or 7.3 Hours/Month

99.5% – 2628 Min/Yr or 43.8 Hours/Yr – 219 Min/Month or 3.65 Hours/Month

99.9% – 525.6 Min/Yr or 8.76 Hours/Yr – 43.8 Min/Month or .73 Hours/Month

99.95% – 262.8 Min/Yr or 4.38 Hours/Yr – 21.9 Min/Month or .365 Hours/Month

99.99% – 52.56 Min/Yr or .876 Hours/Yr – 4.38 Min/Month or .073 Hours/Month

99% uptime sounds like a lot but with 99.95% and 99.99% you would have little or no downtime.

99.5% uptime is sufficent.

It is impossible to get 99.9% uptime.

The ultimate goal is to find a web host that has an uptime guarantee and maintains that level of service. you do need the peace of mind of having your website up and running.