TTL (Time to Live) is a number attached to every DNS record that tells other servers how many seconds they may keep a cached copy of that record before asking for a fresh one. It controls how quickly a change to your domain settings reaches everyone.
How TTL works
When someone types your web address, their device asks a DNS resolver, usually run by their broadband provider or a public service, to find the server’s IP address. The resolver looks up the answer from the Domain Name System and then remembers it, so the next visitor using the same resolver gets an instant reply.
The TTL on the record sets how long that memory lasts. With a TTL of 3600, a resolver keeps the answer for an hour; with 300, for five minutes. Once the time runs out, the resolver asks again and picks up any change you have made. Each record has its own TTL, so your A record pointing to the web server and your MX record pointing to email can expire on different schedules.
What people call “DNS propagation” is mostly this: thousands of resolvers around the country each holding an old answer until their own copy expires. Nothing is being pushed out; the old answers are timing out at different moments.
Why it matters
TTL matters most when you change something: moving to a new host, switching email providers or launching a rebuilt site. Suppose a florist in Brighton moves the website to a new host on a Thursday evening while the A record has a TTL of 86400, a full day. For up to 24 hours some customers reach the old server and some the new one. Orders placed on the old copy can be lost, and form enquiries go to whichever server answered.
Lowering the TTL in advance shrinks that window to minutes. It is one of the simplest pieces of preparation in a site migration, and one of the most often forgotten.
The trade-off is small. A very low TTL means resolvers check more often, which adds a fraction of a second to some first visits. For normal running, an hour or a few hours is a sensible balance.
Common mistakes
- Lowering the TTL at the same time as making the change. Resolvers still hold the old record for the old TTL. Lower it at least one full old-TTL period in advance; if it was 24 hours, do it two days before.
- Forgetting to raise it again. Once the move has settled, set it back to an hour or more.
- Changing nameservers when only a record needed to change. Moving the whole DNS zone to a new provider involves the registry and records you cannot shorten, and changes there can take a day or two to settle everywhere. Pointing an A record usually achieves the same thing faster.
- Testing only from your own computer. Your device and router cache answers too, so you may see the new site while customers still see the old one, or the reverse.
- Switching off the old server too early. Keep it running until traffic to it has stopped.
How to act on it
Log in to wherever your DNS is managed, which may be your domain registrar, your host or a service like Cloudflare, and note the current TTL on your A, CNAME and MX records. If a move is planned, reduce those values to 300 seconds a couple of days before. Make the change, check it from a public DNS lookup tool that queries resolvers in several locations, and keep both servers live until the old one sees no visits.
If you also change nameservers, copy every existing record across to the new provider first, including email and verification records. Timing DNS changes is part of the launch plan I build for website migration SEO.