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NTP Offset Calculator

Work out ntp offset instantly with clear inputs, formula shown and shareable results.

About NTP Offset Calculator

NTP derives offset from four timestamps as ((T2 - T1) + (T3 - T4)) / 2 and round-trip delay as (T4 - T1) - (T3 - T2). The formula assumes the path is symmetric; any asymmetry translates directly into offset error bounded by half the round-trip delay, which is why low and stable latency matters more than raw accuracy of the reference clock.

Formula

NTP offset and delay

offset = ((T2 - T1) + (T3 - T4)) / 2; delay = (T4 - T1) - (T3 - T2); worst-case error = delay / 2

Worked example

With the default values below, NTP Offset Calculator returns Clock offset of -1.500. Change any input above and every figure here is recalculated in your browser.

Inputs used

Client transmit timestamp
1,000 ms
Server receive timestamp
1,042 ms
Server transmit timestamp
1,043 ms
Client receive timestamp
1,088 ms

Results

Clock offset
-1.500 ms
Round-trip delay
87.000 ms
Maximum error from path asymmetry
43.500 ms
Synchronisation status
Well synchronised

Step by step

  1. 1Values used
  2. 2NTP offset and delay
  3. 3Clock offset= -1.500 ms
  4. 4Round-trip delay= 87.000 ms
  5. 5Maximum error from path asymmetry= 43.500 ms
  6. 6Synchronisation status= Well synchronised

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 3 decimal places, 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 does path asymmetry cause error?

The calculation splits round-trip delay equally between the two directions. If one direction is slower, that difference appears as apparent clock offset.

What is the panic threshold?

By default 1000 seconds, above which ntpd exits rather than stepping the clock. Offsets above 128 ms are stepped rather than slewed.

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