TTL stands for time to live: a countdown attached to a piece of data that says how long it may be reused before someone must check for a fresh copy. On websites you mostly meet it in DNS, where it sets how many seconds resolvers may cache your records. Short TTLs make changes appear quickly; long ones make lookups cheaper and steadier.
How DNS uses the TTL value
Every DNS record carries a TTL in seconds. When a resolver fetches your A record with a TTL of 3600, it stores it and answers from memory for the next hour. After that the copy expires, and the next request triggers a fresh lookup to your nameservers. The countdown starts when each resolver fetched the record, not when you last edited it, so different resolvers refresh at different moments.
Common values are 300 (five minutes), 3600 (one hour) and 86400 (one day). Some dashboards show a setting called "Auto", which means the provider picks a value for you.
TTL outside DNS
The same idea shows up elsewhere under the same name. A CDN uses a TTL to decide how long to serve a cached page before asking your server again, and the HTTP Cache-Control: max-age header plays a similar role for the browser cache. At the network level, each IP packet has a TTL field that drops by one at every router hop, so a packet stuck in a loop is discarded rather than circulating forever.
Example: planning a host change
A garden centre plans to switch website hosts on Monday. On Friday, its developer cuts the TTL on the domain's A and www records from 86400 to 300. Old long-lived copies drain out over the weekend. Monday's IP change is then picked up within minutes rather than up to a day. After confirming the new site works, the developer sets the TTL back to an hour.
When you should touch TTL
For most small-business domains, the default is fine and you can leave it alone. It only becomes worth adjusting a day or so before a planned change to your site or email. That is the main lever you have over DNS propagation time.
TTL mistakes
- Lowering it at the moment of the change. Resolvers keep the old record for the old TTL. Lower it at least one full old-TTL period in advance.
- Leaving it very low forever. More lookups mean slightly slower first visits and more dependence on your DNS provider being reachable.
- Setting a week-long TTL on a record you might change. An emergency move would then take days to reach everyone.
- Expecting a TTL change to reach your own laptop instantly. Browsers and operating systems keep small caches of their own; a private window or a phone on mobile data helps when testing.
Related terms
- DNS propagation: the visible effect of TTLs after an edit.
- DNS records: each one carries its own TTL.
- CDN: uses TTLs for cached pages and files.
- Browser cache: the local cache with its own expiry rules.