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DNS TTL Propagation Time Calculator

Work out dns ttl propagation time instantly with clear inputs, formula shown and shareable results.

About DNS TTL Propagation Time Calculator

DNS changes propagate at the speed of the cached TTL, so lowering the TTL must itself happen one full old-TTL period in advance. Compliant resolvers then update within the lowered TTL, but a small share ignore TTLs and cache for hours, which is why the old endpoint must keep serving until the worst-case window has passed.

Formula

Propagation timing

lead time before change = old TTL; propagation = lowered TTL; worst case = over-caching resolver hold time

Worked example

With the default values below, DNS TTL Propagation Time Calculator returns Time for compliant resolvers to update of 1.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Record TTLminimum 1 s
3,600 s
TTL lowered to before the changeminimum 1 s
60 s
Resolvers that over-cacheaccepts 0–100 %
5 %
How long over-caching resolvers hold recordsminimum 0.1 h
24 h

Results

Time for compliant resolvers to update
1.0 min
Worst case including over-caching resolvers
1,440 min
Lead time needed before lowering the TTL takes effect
60 min
Traffic still reaching the old target
5.0%

Step by step

  1. 1Values used
  2. 2Propagation timing
  3. 3Time for compliant resolvers to update= 1.0 min
  4. 4Worst case including over-caching resolvers= 1,440 min
  5. 5Lead time needed before lowering the TTL takes effect= 60 min
  6. 6Traffic still reaching the old target= 5.0

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why lower the TTL in advance?

Because resolvers that already cached the record hold it for the old TTL. Lowering it takes effect only after that period expires.

Should the old endpoint be decommissioned immediately?

No. Keep it serving or redirecting for at least 24 to 48 hours, because some resolvers and hard-coded clients will keep using the old address.

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