TTL, short for time to live, is the number of seconds a DNS record can be saved by other servers before they must check for a fresh copy. Every DNS record has one, and it decides how quickly a change to that record reaches everyone.
How TTL Works
When someone looks up a domain, their DNS service asks the domain’s nameservers for the record and saves the answer. The TTL tells it how long to keep that answer. A record with a TTL of 3600 can be reused for up to an hour, after which the service asks again. Until then, it keeps giving out the saved copy, even if the record has changed.
Common TTL Values
Many DNS hosts default to between one and four hours. Short TTLs, such as 300 seconds, mean changes spread within minutes but cause more lookups. Long TTLs, such as a full day, reduce lookups and can make a site slightly faster, but changes take longer to reach everyone. Records that rarely change, like nameserver records, often use long TTLs.
Using TTL to Make Changes Faster
Before a planned change, such as moving a website to a new host, lower the record’s TTL to 300 seconds at least a day ahead. Once the old, longer TTL has expired everywhere, make the change. Every copy then expires within five minutes. Afterward, raise the TTL again.
The Domibot DNS Propagation Checker shows the remaining TTL at several large DNS services, so you can see exactly when each one will pick up a change.