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Failover Time Budget Calculator

Work out failover time budget instantly with clear inputs, formula shown and shareable results.

About Failover Time Budget Calculator

Failover time is the sum of detection, convergence and service warm-up, and detection is often the hidden cost: default BFD or keepalive timers of several seconds set a floor no amount of fast routing can beat. Sub-second failover requires aggressive detection intervals, which trade against false positives from transient loss.

Formula

Failover budget

total = detection + convergence + service restart; slack = RTO - total

Worked example

With the default values below, Failover Time Budget Calculator returns Total failover time of 20.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Failure detection timeminimum 0 s
3 s
Routing or cluster convergenceminimum 0 s
5 s
Service restart or warm-upminimum 0 s
12 s
Recovery time objectiveminimum 0.001 s
30 s

Results

Total failover time
20.00 s
Slack against the RTO
10.00 s
Dominant stage
Service restart at 60 percent of the budget
RTO assessment
Meets the recovery time objective

Step by step

  1. 1Values used
  2. 2Failover budget
  3. 3Total failover time= 20.00 s
  4. 4Slack against the RTO= 10.00 s
  5. 5Dominant stage= Service restart at 60 percent of the budget
  6. 6RTO assessment= Meets the recovery time objective

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 2 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

How is detection time reduced?

BFD with intervals of tens of milliseconds, or link-state notification from the physical layer. Application-level health checks every 30 seconds cannot support fast failover.

Why does aggressive detection cause problems?

Short timers interpret brief congestion or a control-plane hiccup as a failure, causing unnecessary failovers that are themselves disruptive.

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