DNS Propagation & TTL Calculator
Enter a TTL value to see it in human-readable time and estimate how long a DNS record change takes to propagate. Optionally add your planned change time to get an estimated completion window.
Source: DNS caching/TTL behavior per RFC 1035 and RFC 2181. See the full methodology page. Reviewed: July 2026.
What TTL actually controls
TTL (Time To Live) tells recursive DNS resolvers how long, in seconds, to cache a DNS record before checking with the authoritative nameserver again. It does not control how fast your change reaches every nameserver — that part is usually near-instant once you save it. TTL controls how long already-cached answers around the internet remain valid before resolvers refresh them.
Why "up to 48 hours" is mostly outdated advice
The old "DNS takes 24-48 hours" guidance mostly applied to domain registrar/nameserver delegation changes at the registry level, which do have longer, less predictable caching. For a normal record change (A, CNAME, MX, TXT) on an already-delegated domain, propagation time is bounded almost entirely by the TTL value — once the old TTL expires everywhere, resolvers fetch the new value. A minority of ISP resolvers ignore TTL and cache longer than they should, which is the real source of most "it's not working yet" reports.
Best practice before a planned migration
Lower the TTL to something short (60-300 seconds) well before your cutover — specifically, at least as long as the current (long) TTL in advance, so the short TTL has time to propagate first. Only then make the actual record change. This is the single most effective way to make a DNS cutover fast and low-risk.
Why didn't my DNS change take effect immediately even with a low TTL?
Some resolvers (particularly certain ISP or corporate DNS servers) don't strictly honor TTL and may cache longer. Testing from a public resolver like 1.1.1.1 or 8.8.8.8 directly, or flushing your local DNS cache, usually confirms whether the record has actually updated upstream.
What TTL should I use for records that rarely change?
For stable records (most MX, TXT/SPF records), a longer TTL (3600-86400 seconds) is fine and reduces load on your nameservers. Reserve short TTLs for records you expect to change soon.