DNS TTL Calculator

What TTL controls in DNS

TTL, or time to live, tells every caching DNS resolver around the internet how long it is allowed to keep and reuse a record's answer before it must look it up again from your authoritative nameserver. A higher TTL means fewer lookups and marginally faster resolution for repeat visitors, since more of them hit a cached answer. A lower TTL means resolvers check back more often, which matters when you are about to change a record.

Converting TTL to real-world propagation time

When you change a DNS record, the change is not instant everywhere. Any resolver that already cached the old value under its TTL window will keep serving that old value until its local copy expires, which in the worst case takes as long as the TTL you had set before making the change. This is why lowering TTL in advance of a planned change is the standard way to make propagation faster and more predictable.

Choosing the right TTL for a record type

Records you expect to change soon, like during an active server migration, should use a short TTL such as 300 seconds, set at least 24 to 48 hours ahead of the change so old cached values expire before you flip the switch. Stable, rarely-changed records like a long-established MX or NS record can safely use a much longer TTL, such as 24 or 48 hours, to reduce unnecessary lookup traffic to your nameservers.

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