How to set calibration intervals
There is no universal interval. Set it from risk, manufacturer data and — above all — the instrument's own as-found history.
An interval is a decision about how long you are prepared to trust an instrument between checks. Guidance from ILAC and OIML describes methods, from fixed intervals adjusted on results to statistical control charts, but all of them rest on the same evidence: how the instrument behaved last time.
Inputs
- Manufacturer's stability specification.
- Required tolerance versus the instrument's typical drift.
- Severity of use, environment and handling.
- Consequence of an out-of-tolerance result being discovered late.
- As-found data from previous calibrations: the strongest input.
Adjusting
A run of in-tolerance as-found results with small drift supports lengthening the interval; an out-of-tolerance result shortens it and triggers an impact assessment. Document the rule you use so that intervals are defensible rather than habitual.
Frequently asked questions
- How often should a temperature data logger be calibrated?
- Annually is the most common starting point for loggers in GDP use; the interval should then be adjusted from as-found results and the consequence of an undetected drift.
- Can a calibration interval be longer than one year?
- Yes, if as-found history shows the instrument stays well within tolerance across the interval and the risk assessment supports it. ILAC-G24 describes methods for adjusting intervals on evidence.
- Does the manufacturer set the calibration interval?
- The manufacturer's stability specification is an input; the interval is the user's decision under ISO/IEC 17025 clause 6.4 and GxP expectations.
References
- [1]ILAC-G24 / OIML D 10: Guidelines for the determination of calibration intervals of measuring instruments
- [2]ISO/IEC 17025:2017 — General requirements for the competence of testing and calibration laboratories
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
Have a question on this topic?
Ask ValiTrac AI and see the evidence and calculation behind the answer.
Ask ValiTrac AIFree calculator: Guard band / decision rule
Turn a tolerance and an expanded uncertainty into acceptance limits under ILAC-G8 rules, and see the false-accept and false-reject risks.
Open the calculatorCalibration on ValiTrac
Support calibration workflows, uncertainty budgets and certificate generation.
See the calibration workflowRelated articles
As-found vs as-left
Why both sets of readings matter, and what to do when the as-found data are out of tolerance.
Calibration, adjustment and verification are different things
Calibration measures; adjustment changes the instrument; verification compares against a requirement. Mixing them up leads to lost as-found data and unsupported claims.