Last Updated on September 25, 2025 by Melissa Lazaro

Introduction: Why Audit Man-Days Matter More Than You Think

When companies get their first ISO 13485 certification quote, one of the biggest shocks is the number of audit days listed. I’ve had clients call me saying, “Why did one CB quote us 3 days and another 6? Are they just making this up?”

Here’s the deal: audit man-days are the single biggest driver of your certification costs. It’s simple math—daily auditor rate × number of days = the bulk of your invoice. If you don’t understand how those days are calculated, you’ll always feel like you’re at the mercy of the certification body.

In this article, I’ll break down what “audit man-days” actually mean, the rules behind how CBs calculate them, and the levers you can use to challenge or validate a quote. By the end, you’ll know how to spot if your company is being over- or under-quoted—and how to use that knowledge to plan your certification budget with confidence.

What “Audit Man-Days” Actually Mean

An audit man-day is basically one auditor working for one full day. Sounds simple, right? But here’s why it matters so much:

• The number of audit days you’re assigned directly controls how much you pay.

• Every extra day = another full day’s billing.

• It’s not just the initial certification audit—you’ll pay man-days again during surveillance and recertification audits.

Pro Tip: Always ask your CB how they calculated the audit days in your quote. The best CBs will give you a clear breakdown.

Common Mistake: Thinking that fewer audit days is always better. I worked with a company that pushed to reduce their audit to the bare minimum. The CB agreed, but the audit was so rushed that gaps were missed, and regulators flagged issues later. That “saving” ended up costing them more.

Now that we’ve defined what an audit man-day is, let’s talk about the rules certification bodies are supposed to follow when they calculate those numbers.

The Rules Behind the Calculator (IAF MD 5 Explained Simply)

Certification bodies don’t just pull audit days out of thin air. They’re supposed to follow a global rulebook called IAF MD 5 (short for International Accreditation Forum Mandatory Document 5). Think of it as the “calculator” for how many days you get audited.

Here’s how it works in plain language:

• Employee Count → The main driver. The more staff you have, the more time auditors need to check your QMS.

• Complexity of Operations → Designing, manufacturing, and distributing is more complex than just one of those activities, so you’ll get more audit days.

• Scope of QMS → The wider your scope (e.g., multiple product families or sites), the longer the audit.

• Risk Level → Higher-risk devices = more scrutiny.

• Audit Type → Stage 1, Stage 2, surveillance, or recertification all have slightly different rules.

Quick Example:

• A small startup with 12 employees might be assigned 3 audit days.

• A medium-sized company with 250 employees across two sites might face 10–12 days.

• A large multinational with 1,000+ employees could be looking at 15+ days spread across multiple auditors.

Common Pitfall: Many companies assume the CB can “negotiate” the audit days freely. In reality, they’re bound by IAF MD 5. Where CBs differ is in how strictly they interpret the rules.

Pro Tip: Ask your CB to show you the IAF MD 5 table they used. If they hesitate, that’s a red flag. A good CB will happily walk you through the calculation.

Factors That Change the Audit Day Count

Even with IAF MD 5 as the “rulebook,” the actual number of audit days can still vary. That’s because several factors push the calculation up or down. If you don’t know these, you can end up paying for days you didn’t really need.

4.1 Number of Employees

This is the big one. The tables in IAF MD 5 use staff count as the main starting point. More employees = more audit time.
Pro Tip: Make sure you’re clear on who counts as an “employee.” Contractors or part-time staff don’t always need to be included, but some CBs add them by default.

4.2 Scope of Your QMS

Design + manufacturing + distribution = more audit time than just manufacturing. Each additional process adds hours.
Pitfall: Companies sometimes include extra activities “just in case” during application. That can lock you into more audit days than you need.

4.3 Risk Class of Devices

Higher-risk devices (like implants) require deeper audits. Lower-risk devices (like accessories) mean fewer audit days.

4.4 Multi-Site Operations

One site is straightforward. Multiple sites? Each one adds time. Even small satellite offices can trigger extra days if they handle important processes.

4.5 Outsourced Processes

Even if you outsource, you’re still responsible for oversight. Auditors may add days to check how you control suppliers.
Example: A client outsourced sterilization. Their CB added half a day to verify supplier management, even though the company didn’t do sterilization in-house.

4.6 Compliance History

If you’ve had major nonconformities in the past, CBs may increase audit time to recheck those areas. On the flip side, a clean track record sometimes helps reduce days at surveillance.

How Certification Bodies Apply the Calculator Differently

If IAF MD 5 is the “rulebook,” you might wonder: why do two certification bodies give different audit day counts for the same company? The answer is interpretation.

5.1 Conservative vs. Flexible Approaches

Some CBs stick to the strictest reading of the rules—they’ll round up every borderline case. Others take a more practical approach, rounding down where it makes sense. That’s why one quote might say 5 days while another says 7 for the exact same operation.

Pro Tip: If you’re on the edge of an employee bracket (say 48 staff vs. 51), ask your CB if they rounded up or down. That can make the difference of an entire audit day.

5.2 Outsourced Activities

One CB may decide your outsourced sterilization process needs an extra audit day. Another might just add a few hours. Same company, two different outcomes.

5.3 Auditor Availability

Here’s something most companies don’t realize: scheduling also plays a role. If a CB doesn’t have local auditors available, they may “bundle” audit days differently—sometimes stretching them over extra days. That adds cost.

Common Pitfall: Accepting a higher audit day count without questioning it. I worked with a client who got quotes for 6 and 8 days from two CBs. When we pushed back and asked for justification, the 8-day CB revised their quote to 6.5. Just asking the question saved real money.

5.4 Multi-Site Interpretation

Some CBs require full audits at every site. Others use a sampling method allowed under IAF MD 5. That can cut multiple days if applied correctly.

Using the Calculator to Your Advantage

Understanding how audit man-days are calculated isn’t just about curiosity—it’s a way to protect your budget and avoid overpaying. Once you know the rules, you can challenge numbers that don’t make sense.

6.1 Do a Rough Self-Check

You don’t need to be an auditor to get a ballpark figure. Start with your employee count, scope (design, manufacturing, distribution), and number of sites. Then compare it against the IAF MD 5 tables. If your CB’s quote looks way off, ask them why.

Pro Tip: If two CBs give very different audit day numbers, use IAF MD 5 as your reference point in discussions. It shows you’ve done your homework.

6.2 Ask for Justification

Don’t be shy about asking, “Can you walk me through how you calculated the audit days?” A credible CB should be able to explain their reasoning. If they hesitate or give vague answers, that’s a warning sign.

6.3 Negotiate Borderline Cases

If your staff count is right on the edge of a threshold (say 50 employees vs. 51), push for the lower bracket if it’s justified. That one headcount difference can mean an extra audit day.

Common Pitfall: Accepting the CB’s number as final without question. I’ve seen companies save thousands just by challenging one or two “extra” days.

6.4 Plan Ahead to Reduce Future Costs

If you know you’ll add staff or expand scope, factor that in. Otherwise, you may get hit with a surprise increase in audit days mid-cycle.

Real Example: A client grew from 40 to 70 employees during their certification cycle. Their audit days jumped by two—adding more than €4,000 in costs. If they had planned and negotiated upfront, the increase could have been smoother.

FAQs on ISO 13485 Audit Man-Days

7.1 Is there a public ISO 13485 audit man-day calculator I can use?

Not an official one. The real “calculator” is IAF MD 5, which certification bodies must follow. Some CBs publish simplified versions on their websites, but they’re usually just rough guides. You can still do a decent self-check using your employee count and scope.

7.2 Can audit days ever be reduced after I get the quote?

Yes, sometimes. If you can show a narrower scope, combine audits (for example ISO 9001 + ISO 13485), or clarify that certain staff/activities don’t need to be counted, you may be able to cut audit days. But reductions always need to stay within IAF MD 5 rules.

7.3 Why won’t some certification bodies negotiate audit days at all?

It usually comes down to their accreditation body. Some CBs take a very strict approach to avoid any risk of being accused of under-auditing. Others have more flexibility in interpretation. If a CB says “no negotiation,” it’s not always stubbornness—it may just be their policy to stick rigidly to the rulebook.

Conclusion: Turning the Audit Man-Day Calculator Into an Advantage

Audit man-days can feel like a black box when you first see them on a certification quote—but once you understand how they’re calculated, they stop being intimidating and start becoming a tool you can use to your advantage.

Here are the key points to remember:

• Audit man-days are the main driver of ISO 13485 certification costs.

• The official calculator (IAF MD 5) sets the rules, but CBs interpret them differently.

• Employee count, scope, risk class, and sites are the biggest factors.

• Always ask your CB to justify their calculation—it’s your right as the client.

• Small details, like clarifying headcount or scope, can save you audit days (and thousands of euros).

I’ve seen companies overpay simply because they didn’t know they could ask questions. On the flip side, the clients who understood the man-day rules went into negotiations confident and avoided unnecessary costs.

Next Step: If you’ve already received a quote, pull out the IAF MD 5 rules (or a simplified calculator) and check the numbers for yourself. If something looks off, push back and ask for a breakdown. It could be the easiest money you save in your certification journey.