DNS Propagation Monitor Calculator

Calculator Inputs

Domain

Record name or host

Record type

Expected record value

Old TTL (seconds)

New TTL (seconds)

Time since change (minutes)

Total probe locations checked

Locations seeing the new value

Probe rounds completed

Authoritative sync (%)

Cache decay factor

Polling interval (minutes)

Target completion (%)

This calculator models DNS spread from observed resolver checks and cache timing. It does not perform live global DNS queries by itself.

Formula Used

1) Observed Adoption
(Locations Seeing New Value / Total Locations Checked) × 100

2) Theoretical Cache Release
100 × [1 - e^(-Cache Decay Factor × Time Since Change ÷ Old TTL Minutes)]

3) Weighted Propagation
(0.55 × Observed Adoption) + (0.25 × Theoretical Cache Release) + (0.20 × Authoritative Sync)

4) Confidence Score
This score combines sample size, probe rounds, and authoritative alignment. More locations and repeated checks improve confidence.

5) Estimated Remaining Time
The model solves the decay curve to reach your target completion level, then adjusts remaining time when observed adoption trails the cache model.

Important TTL note
Lowering the TTL after a change helps future cache entries, but already cached records generally remain governed by the old TTL.

How to Use This Calculator

Enter the domain, record host, record type, and the value you expect resolvers to return.
Provide the old TTL and new TTL. The old TTL strongly affects current propagation speed.
Enter minutes since the DNS change was published.
Add how many resolver locations you checked and how many already show the new answer.
Set probe rounds, authoritative sync, polling interval, and cache decay factor for your environment.
Submit the form. The page shows the result below the header and above the form.
Review weighted propagation, confidence, consistency, risk, and the chart before making a cutover decision.
Use the CSV and PDF buttons to export a simple monitoring report.

Example Data Table

Minute Mark	Theoretical Cache Release (%)	Example Observed Adoption (%)	Locations on New Value	Locations Still Stale
0	0.0	7.7	2	22
15	25.0	29.7	7	17
30	43.7	46.2	11	13
60	68.3	67.8	16	8
120	90.0	86.9	21	3
180	96.8	92.9	22	2

This example table is illustrative. Your live inputs may produce different adoption patterns.

FAQs

1) What does this calculator actually monitor?

It estimates DNS propagation progress from probe coverage, resolver adoption, TTL timing, and authoritative alignment. It is a planning and monitoring model rather than a live DNS testing network.

2) Why does the old TTL matter more than the new TTL?

Resolvers that cached the earlier answer normally keep it until that older TTL expires. Lowering the TTL after the change does not instantly shorten those already existing cache entries.

3) What is the cache decay factor?

It controls how quickly the theoretical model releases stale caches. Larger values make the curve rise faster. Use conservative values when resolver behavior is uneven or unpredictable.

4) How should I interpret weighted propagation?

Weighted propagation blends observed resolver results, modeled cache expiry, and authoritative sync. It helps summarize progress into one operational metric for release planning.

5) Why can observed adoption lag the model?

Resolvers may refresh at different times, some probes may share recursive infrastructure, and geographic samples can be uneven. Authoritative mismatches can also delay full adoption.

6) Is 100 percent propagation ever guaranteed?

Not perfectly. Some caches, forwarders, client systems, or corporate resolvers may trail behind. Most teams use a practical threshold such as 95 percent or 99 percent.

7) When should I trust the confidence score?

Trust it more when you check many locations across multiple rounds and your authoritative servers are fully aligned. Small samples naturally reduce certainty.

8) Can this page replace external DNS checkers?

No. It complements them. External checkers provide live observations, while this calculator helps quantify progress, explain delays, and estimate the remaining propagation window.