You can really see if your web host delivers on their 99.9% uptime guarantee by installing a website monitor. A website monitor will let you know when your website is down. There are free and premium website monitors out there.
SiteUptime offers both free and premium plans for website monitoring. I’ve been using SiteUptime for a few years now, and I’ve enjoyed their service. I get notified via email when my website goes down, and SiteUptime checks my site every 30 minutes. You can have SiteUptime check your website more frequently with a premium plan.
Also, every month, I get an email notifying me how many times my site has been down. Please note, that I’m not being paid to plug SiteUptime. You don’t have to use SiteUptime, but you do want to find a site monitoring service to find out how much traffic you are missing out on.
Once you do have a site monitor installed on your website, you want to make sure your site is up 99.9%. Wait for a couple of months to get more accurate data. If it’s below 99.9%, you may want to find a different hosting company.