DNS TTL Propagation Calculator
Turn a DNS record TTL (time-to-live) in seconds into human-friendly minutes and hours, and see how long a change can take to fully propagate. The worst-case propagation window is set by the PREVIOUS TTL still sitting in caches, not the new one.
Enter Values
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How to use this calculator
- Enter the record's TTL in seconds (e.g. 3600 for one hour).
- Optionally enter the previous/old TTL to report the true worst-case propagation window from before the change.
- Read the minutes, hours and human-readable duration, and plan changes around the worst-case time.
How it works
TTL in minutes = seconds ÷ 60 and TTL in hours = seconds ÷ 3600. The human-readable duration breaks the seconds into days, hours and minutes. Because resolvers cache an answer for its whole TTL, a change is not global until every cache holding the OLD value expires — so the worst-case propagation time equals the previous TTL if you supply it, otherwise the current TTL.
Worked example
Worked example. A record with TTL 3600 is cached for 60 minutes (1 hour), shown as '1 h 0 min'. Dropping it to 300 caches it for just 5 minutes, so future changes propagate far faster.
Common mistakes
- Assuming a change is instant once you save it — old cached answers linger for up to the previous TTL.
- Lowering the TTL at the same moment as the change instead of well beforehand, so old high-TTL copies are still cached.
- Trusting a very low TTL completely — some resolvers, forwarders and browsers enforce their own minimums and ignore it.
Frequently asked questions
How long does DNS propagation really take?
Up to the previously-cached TTL. If a record had a 24-hour TTL and you change it, some resolvers may keep serving the old value for close to 24 hours until their cache expires.
What TTL should I use before a migration?
Lower the TTL to something short like 300 seconds (5 minutes) a day or two before the change, make the change, verify it, then raise the TTL back to an hour or a day to reduce query load once everything is stable.
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Tip: Enter any known values to calculate the remaining results.
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