One of the biggest surprises for certification bodies preparing for F accreditation is just how much time the audit actually takes. It’s not uncommon for an assessment to stretch longer than expected simply because the team underestimated the number of assessor days required.
I’ve seen this happen too many times — organizations budgeting for a three-day audit that turns into five or six. Not only does that mean higher fees, it also disrupts schedules and adds unnecessary stress.
This guide breaks down how man-days are calculated, what drives audit duration, and how to estimate it accurately. Once you understand the logic behind the numbers, you can plan your resources, budget smarter, and even negotiate better with your accreditation body.
What “Audit Man-Days” Mean in the ISO/IEC 17024 Context
The term “man-day” simply means one assessor working for one full day. So, if three assessors work for two days, that’s six man-days — not two. It’s a small detail, but it completely changes your calculation.
Pro Tip: Always clarify how your accreditation body handles partial days. Some round up even a half-day to a full one.
Common Mistake: Mixing up assessor days with calendar days. If two assessors visit for two days, that’s four man-days total — not two.
Key Factors That Influence ISO/IEC 17024 Audit Duration
Not all certification bodies are created equal, and neither are their audits. Several factors quietly shape your total man-days:
Number of certification schemes — each one might require separate witnessing.
Complexity of exams and competence criteria.
Number of competence areas or job roles under each scheme.
Geographic spread — multiple offices or testing sites increase travel and time.
Subcontracted activities — if you outsource any part of assessment or exam delivery, expect extra assessor days.
In my experience, a single-scheme body might need around 3–4 man-days for the initial assessment. Add a few more schemes or extra locations, and you’re quickly at 10–15 man-days.
Pro Tip: Start small. Accredit your most critical scheme first, then expand later. Pitfall: Trying to include every possible scope upfront — it inflates audit duration and costs unnecessarily.
Step-by-Step: How to Estimate Your Man-Days
Let’s make this practical. Here’s how you can estimate your own audit duration before the quote arrives:
Step 1: List all your certification schemes and the competence areas for each. Step 2: Note how many sites or exam locations you operate. Step 3: Check whether each scheme requires a separate witness assessment. Step 4: Add days for document review, onsite verification, and follow-up. Step 5: Multiply the number of assessors involved.
You can use this simplified formula:
Total Man-Days = (Base Days per Scheme × Number of Schemes) + Witness Days + Travel/Review Days
Pro Tip: Create a simple spreadsheet for this — it becomes your own calculator. Example: If your base scheme takes 3 days, you have 2 schemes, plus 2 days for witnessing and 1 for document review, your total is 3×2 + 2 + 1 = 9 man-days.
Typical Audit-Duration Benchmarks
Based on what I’ve seen across different accreditation bodies, here’s a practical range to work with:
Type of Certification Body
Initial Assessment
Surveillance
Single-scheme (simple competence)
3–4 man-days
1–2 man-days
Multi-scheme (2–3 scopes)
6–8 man-days
3–4 man-days
Large or multi-site body
10–15 + man-days
5–7 man-days
These numbers aren’t fixed — they depend on your scheme design, competence criteria, and assessor availability.
One of my clients under ANAB trimmed their surveillance duration from 6 to 4 man-days simply by merging two similar schemes into one and consolidating witness sessions. That’s the kind of efficiency you should aim for.
Pro Tip: When scheduling, align related schemes in the same audit window to avoid paying twice for assessor travel.
How to Use an ISO/IEC 17024 Audit-Duration Calculator
An audit-duration calculator helps take the guesswork out. Instead of juggling spreadsheets, you input your key details and get an instant estimate.
Most calculators (like the one we use at QSE Academy) ask for:
Number of certification schemes
Competence areas per scheme
Assessment sites
Witness requirements
Type of assessment (initial or surveillance)
The output gives you:
Estimated total man-days
Suggested audit schedule
Cost projection based on typical assessor-day rates
Pro Tip: Use the calculator as a baseline — then cross-check with your accreditation body’s published policies. They may have minimums or rounding rules that slightly adjust your results.
Every extra man-day adds cost — assessor fees, travel, accommodation, and per diems. But underestimating can be just as expensive. A rushed audit often leads to findings that trigger repeat visits or follow-ups.
Getting your calculation right means fewer surprises and more control. You’ll be able to:
Budget with precision
Schedule audits efficiently
Avoid unnecessary assessor-day extensions
A client I worked with recalculated their SANAS audit plan and realized two redundant assessor days were built into the quote. By clarifying the scope and combining witness activities, they saved nearly USD 4 000. That’s the value of understanding your man-days.
FAQs – ISO/IEC 17024 Man-Day Calculations
Q1: Can I shorten audit man-days by limiting my scope? Absolutely. Narrowing your scope to core certification schemes reduces witness sessions and assessor days — and you can always expand later.
Q2: Do all accreditation bodies publish man-day tables? Not always. ANAB and IAS provide general guidance, but SANAS, UKAS, or DAC might calculate each case individually. Always ask for their policy upfront.
Q3: What’s the difference between accreditation and certification man-days? Accreditation audits focus on your management system, impartiality, and competence — they’re broader. Certification audits focus on assessing candidates under your scheme.
Plan Smarter, Audit Smoother
Understanding how audit man-days are calculated isn’t just about numbers — it’s about control. When you know what drives duration, you can plan ahead, reduce costs, and make the accreditation process far less stressful.
In my years helping certification bodies across industries, one thing’s clear: well-planned audits run faster, cheaper, and cleaner.
If you’d like access to QSE Academy’s ISO/IEC 17024 Audit-Duration Calculator or need help estimating your next accreditation audit, reach out — we’ll tailor one specifically for your scope and accreditation body requirements.
Melissa Lavaro is a seasoned ISO consultant and an enthusiastic advocate for quality management standards. With a rich experience in conducting audits and providing consultancy services, Melissa specializes in helping organizations implement and adapt to ISO standards. Her passion for quality management is evident in her hands-on approach and deep understanding of the regulatory frameworks. Melissa’s expertise and energetic commitment make her a sought-after consultant, dedicated to elevating organizational compliance and performance through practical, insightful guidance.
