Maintenance & Reliability worked example

Reliability Percentage at 99% target reliability: a worked example

What does the result look like when target reliability reaches 99%? The full calculation is worked below with real intermediate numbers. Use it when a reliability study has already converted failure rate and mission time into a survival fraction that needs a percent display.

The inputs for this scenario

  • Equivalent successful missions at time t: 97 missions (unchanged)
  • Mission sample basis: 100 missions (unchanged)
  • Target reliability: 99 % (raised for this scenario; the documented default is 98)

Working through the calculation

  • Applying the documented formula (Reliability percentage = equivalent successful missions at time t ÷ mission sample basis × 100) to the inputs above produces each figure below.
  • At this operating point the engine returns 97 % for mission reliability, the number this scenario is built around.
  • At this operating point the engine returns 2 points for gap to reliability target.
  • At this operating point the engine returns 97 count for equivalent successful missions.
  • At this operating point the engine returns 100 count for mission sample basis.

How this compares with the baseline

  • Against the tool's baseline example, where target reliability sits at 98% and the headline result is 97 %, this scenario lands almost exactly on the baseline at 97 %.
  • A figure at this level is achievable when target reliability is genuinely sustained, not just peaked for a shift. It is a point estimate tied to a specific mission length t; it carries no confidence interval and small sample sizes can make the figure statistically fragile.

Results at a glance

  • Mission Reliability: 97 % (headline result)
  • Gap to Reliability Target: 2 points
  • Equivalent Successful Missions: 97 count
  • Mission Sample Basis: 100 count

Run it with your numbers

  • Every input above is editable in the live Reliability Percentage calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.