Calculator
Example data table
| Scenario | Old TTL | Negative TTL | Authoritative delay | Safety buffer | Estimated full window |
|---|---|---|---|---|---|
| Modify A record after lowering TTL in advance | 300 s | 900 s | 7 min | 15 min | 27 min |
| Create record after prior NXDOMAIN | 0 s | 900 s | 5 min | 10 min | 30 min |
| Delegation change with parent TTL impact | 3600 s | 900 s | 10 min | 30 min | 2 days, 40 min |
Formula used
Effective Old TTL = Current TTL, when no pre-lowering exists.
Effective Old TTL = max(Pre-lowered TTL, Current TTL − Hours Since Lowered × 3600), when TTL was lowered earlier.
Modify or delete existing record = Effective Old TTL
Create after NXDOMAIN = Negative TTL
Delegation change = max(Effective Old TTL, Parent Zone TTL)
Authoritative Delay = Provider Push Delay + Secondary Sync Delay + DNSSEC Signing Delay
Typical Delay = Authoritative Delay + (Cache Window × Cache Impact Multiplier × Resolver Factor)
Full Propagation Delay = Authoritative Delay + Cache Window + Safety Buffer
This model estimates visibility timing, not guaranteed resolver behavior. Real networks differ by cache refresh policy, resolver software, CDN layer, and monitoring location.
How to use this calculator
- Choose the DNS record type and the kind of change.
- Enter the publish time when the new zone data goes live.
- Fill in current TTL, new TTL, and negative TTL values.
- Add provider, secondary sync, and DNSSEC delays if they apply.
- Enter any pre-lowered TTL and how long ago you lowered it.
- Set the estimated cached audience and resolver profile.
- Press the calculate button to see uncached, typical, and full timing.
- Use CSV or PDF export for change plans, reports, or reviews.
8 FAQs
1. Does DNS propagation mean the same thing everywhere?
No. Different resolvers expire cached answers at different times. Authoritative servers may already be updated while some users still receive older cached data.
2. Why does lowering TTL earlier matter?
Lowering TTL in advance reduces the old cache lifetime before the actual record edit. That can shrink the worst-case stale-answer window during cutover.
3. What is negative TTL?
Negative TTL controls how long resolvers may cache a missing-answer response, such as NXDOMAIN. It matters when creating a record that did not exist before.
4. Why include provider push delay?
Some DNS platforms take time to publish changes across their authoritative network. That delay happens before uncached resolvers can see the new answer.
5. What does the conservative full propagation time represent?
It is the model’s safest estimate for broad visibility. It adds authoritative delay, the relevant cache window, and an extra operational buffer.
6. Are delegation changes slower than normal record edits?
Often yes. Parent-zone TTL and resolver behavior can make nameserver or delegation changes slower than a simple A, AAAA, or TXT record edit.
7. Does the new TTL control old caches?
No. Old cached answers usually follow the TTL that existed when they were stored. The new TTL mostly affects fresh cache entries after the rollover.
8. Should I verify from one location only?
No. Test from multiple networks or public resolvers. A single probe can show the new answer while other regions still see stale cached data.