Tachograph Calibration: How Often, Who Does It, and What to Check

Tachograph calibration is one of the compliance tasks most likely to slip through the cracks. Unlike a driver card download — which has a hard 28-day deadline on a rolling clock — calibration is due every 2 years per vehicle. That long interval is exactly what makes it easy to miss: the next due date feels remote until it's suddenly overdue.

This guide covers what calibration involves, who can do it, how to track the deadline, and what to do if you've let it lapse.

General guidance, not legal advice. Requirements for tachograph calibration are set by UK-retained EU regulation and supplementary DVSA guidance. Always verify current requirements against the latest DVSA and Traffic Commissioner guidance for your licence type and vehicle category.

Why Calibration Is a Legal Requirement

The DVSA tachographs overview identifies calibration and maintenance of tachograph equipment as a key operator responsibility. The requirement exists because tachograph data is used for enforcement — if the recording equipment hasn't been calibrated to the correct standard, the data it produces may not accurately reflect actual driver behaviour.

A tachograph that has never been calibrated or is running out-of-calibration isn't technically compliant, even if it's recording data. DVSA examiners at roadside stops check the calibration plaque (the metal plate attached to the tachograph head) to confirm calibration is current. At an operator visit, DVSA will check calibration records across your fleet.

The goods vehicle operator licensing guide notes transport managers must ensure "tachograph calibrations are up to date and displayed" — this is a named transport manager responsibility, not a background administrative task.

When Calibration Is Due

For digital tachographs (the standard across new vehicles since 2006), calibration is required:

• On initial installation in a vehicle
• Every 2 years thereafter
• Following any major repair that affects the tachograph or the vehicle's speed measurement system
• After replacement of the vehicle's wheel or tyre size, which changes the odometer constant
• After any tampering or suspected damage to the tachograph head or its seals
• When the vehicle registration changes (re-registration requires a new calibration record)

For smart tachographs (required in new vehicles from June 2019 — the second-generation digital type), the same 2-year calibration interval applies.

The calibration certificate and associated plaque show both the date of calibration and the date the next calibration is due. The plaque is physically attached to the tachograph head and must remain legible. If a plaque is missing or damaged, the vehicle is non-compliant regardless of whether the calibration was done on time.

Who Can Calibrate a Tachograph

Calibration must be carried out by a DVSA-approved tachograph centre. You cannot calibrate a tachograph yourself, and an unapproved workshop cannot legally do it either.

Approved centres are workshops that have been assessed and authorised by DVSA to carry out tachograph installation, calibration, repair, and sealing. They hold specialised equipment and authorisation to issue calibration plaques and certificates. Using an unapproved workshop isn't just non-compliant — any certificate issued by an unapproved workshop has no legal standing.

To find an approved centre, search for "DVSA approved tachograph centre" — most major commercial vehicle service networks (truck dealerships, independent HGV workshops) hold DVSA tachograph approval. Confirm approval before booking.

What Calibration Actually Involves

At an approved centre, the calibration process typically includes:

1. Reading the tachograph data — before calibration, a full download of the vehicle unit data is taken to preserve the record
2. Checking the tachograph constants — the centre verifies the programmed tyre/wheel constant against the vehicle's actual measurements
3. Comparing against DVSA reference — the tachograph's speed and distance recording is compared against a measured reference
4. Checking the internal clock — the tachograph's time must be accurate (set to UTC for the recording, not local time); deviations are corrected
5. Inspecting the seals — broken or damaged seals are replaced; any evidence of tampering is documented
6. Issuing the calibration plaque and certificate — the new plaque is fixed to the tachograph head; a written certificate is issued to the operator

The whole process typically takes a few hours. Vehicles with smart tachographs may take longer if the GNSS (GPS) antenna or the DSRC unit (the short-range communication system used for remote roadside data exchange) needs checking alongside the main unit.

What to Look For on the Calibration Plaque

The calibration plaque is your first check at any roadside inspection. It shows:

• The date of the most recent calibration
• The unique identifier of the approved tachograph centre
• The vehicle's w-factor (wheel circumference constant) and l-value (effective tyre circumference)

When the calibration is current, the plaque's date plus 24 months gives you the next due date. Get in the habit of noting this on your compliance calendar when each vehicle is calibrated.

Seals are a separate visual check: the tachograph head should have intact seals over the case screws and cable entry points. Broken seals are a red flag — they suggest the unit was opened after calibration, which voids the calibration and requires re-inspection.

Tracking Calibration Deadlines

For a fleet of 2-3 vehicles, calibration dates are easy to lose track of because they're vehicle-specific and staggered — each vehicle has its own 2-year clock running from its last calibration date.

The simplest tracking method: add each vehicle's calibration due date to your compliance calendar with a 3-month advance reminder. If you use a fleet compliance tool, check whether it tracks tachograph calibration expiry (many do — see our fleet compliance software guide for what to look for). For a manual approach, your vehicle maintenance planner is the right place — see our vehicle maintenance planner guide for how to structure your inspection tracking.

Don't wait until the due date to book. Approved centres that service HGV fleets often have lead times of a week or more. Book at least 4 weeks before the calibration is due.

What If Calibration Has Lapsed

If a vehicle's calibration is overdue, the right course of action is:

1. Take the vehicle off the road if calibration is significantly overdue (more than a few days). A vehicle operating with an out-of-calibration tachograph is in breach and adds OCRS points to your record.
2. Book the calibration immediately at an approved centre. Don't delay.
3. Download all tachograph data from the vehicle unit before calibration (calibration resets some internal counters).
4. Document the lapse — record when you discovered the lapse, what steps you took, and the date calibration was completed. This record demonstrates good faith if the issue is raised at a DVSA visit.
5. Review your tracking system to understand how the deadline was missed, and fix it. An isolated lapse is less serious than a pattern of missed deadlines — DVSA and traffic commissioners look at whether your compliance management systems are functioning.

An overdue calibration found at a roadside check is a roadworthiness offence. It adds a traffic offence to your OCRS score and can contribute to a DVSA operator premises visit if combined with other findings.

Cost

Tachograph calibration costs vary by centre and region. As a rough guide, calibration at an approved workshop typically ranges from £60 to £150 per vehicle, though prices vary and you should confirm directly with your chosen centre. Smart tachograph calibrations may cost more due to the additional system checks.

The cost of a calibration is trivial compared to the cost of an OCRS infringement or a Traffic Commissioner inquiry. Budget for it annually as a fixed compliance cost.

Calibration vs Inspection vs Repair

Calibration, inspection, and repair are three distinct types of tachograph workshop activity:

• Calibration (every 2 years): checking and recording the tachograph's accuracy against standards; issuing the plaque and certificate
• Inspection (typically every 6 years, or on an approved centre's recommendation): a more thorough internal check of the tachograph unit's mechanical and electronic components
• Repair: fixing a defective tachograph; any repair involving opening the unit must be followed by a new calibration

For most operators, calibration is the only scheduled tachograph centre visit. Inspection and repair are event-driven.

Tachograph Calibration and Your O-Licence

The O-licence compliance checklist covers calibration as a named compliance item alongside PMI intervals, MOT expiry, and driver CPC records. A DVSA vehicle examination at your operating centre will pull calibration records for all authorised vehicles. Systemic calibration failures — more than one vehicle overdue, or a pattern of late calibrations — are taken seriously by traffic commissioners as evidence of inadequate transport management.

The calibration plaque, the calibration certificate, and your booking/tracking record together form the audit trail. Keep the certificate (don't just rely on the plaque) and file it with each vehicle's compliance folder.

Sources

• Tachographs overview — GOV.UK
• Drivers' hours — GOV.UK
• Goods vehicle operator licensing guide — GOV.UK
• Operator Compliance Risk Score — GOV.UK