Insights · Blog · Licensing · May 8, 2026

Base + Attach: the Microsoft licensing lever almost no one uses correctly.

Microsoft Dynamics 365 has a licensing mechanic that is documented on page 6 of the Microsoft Licensing Guide — and that we find misconfigured at every third client. It's called Base + Attach. Anyone who understands it often saves five- to six-figure amounts per year.

The Microsoft Dynamics 365 license model is not intuitive. Some licenses are named, others are capacity-based, and some obscure in the marketing materials that they can be acquired significantly cheaper — if you know how. Base + Attach is one of the three mechanisms in which Microsoft gives money back when the customer configures the license logic correctly. The other two are operations order lines (for transactional multiplexing scenarios) and device licenses (for shared machines). Today is only about Base + Attach.

In the past two years we have looked into license configurations at around 40 mid-market companies in audit sessions. In about 14 cases, Base + Attach was not running or running only partially. In one of these cases — a wholesaler with 90 sales reps — the correction saved USD 27,000 per year. That's right. That's more than the list price of some premium licenses.

How Base + Attach works

Microsoft says it in the Licensing Guide so directly that it's easy to miss:

"When purchasing multiple Dynamics 365 applications for a single user, the first application license must be the highest priced license (a.k.a. base license) for the named user. Every full-access user must have a base license." (Licensing Guide May 2026, p. 6)

Translated: when a user needs multiple Microsoft Dynamics 365 apps, the first license is the most expensive one (the base) — all further licenses are billed at the attach price, which is significantly lower. Microsoft explicitly clarified this again in the May 2026 guide: "Base and attach licenses are identical in their core capabilities and are only differentiated in price."

Concretely, this means: Sales Enterprise as base costs USD 95 per user per month. If the same user additionally needs Customer Service Enterprise, this second license does not cost another USD 95 — but USD 20. That is a reduction of around 78 %.

The most important Base and Attach prices at a glance

List prices USD per user per month, as of Licensing Guide May 2026:

Application	Base	Attach	Difference
Sales Enterprise	$95	$20	−$75
Customer Service Enterprise	$95	$20	−$75
Field Service	$95	$20	−$75
Sales Premium	$135	$50	−$85
Customer Service Premium	$135	$50	−$85
Finance	$210	$30	−$180
Supply Chain Management	$210	$30	−$180
Project Operations Core	$120	$30	−$90
Business Central Premium	$100	$20	−$80

Note: list prices per Microsoft pricing page. Actual prices in the CSP model depend on the reseller. Values rounded, validated against the May 2026 guide.

Example 1: 30-person sales team with Sales + Service

A mid-market company with 30 sales reps, all of whom use both Sales Enterprise and Customer Service Enterprise — a typical setup for inside sales teams that also handle complaints directly.

Incorrect configuration (which we often see): 30× Sales Enterprise + 30× Customer Service Enterprise, both as full-price licenses. 30 × ($95 + $95) = $5,700/month.

Correct configuration (Base + Attach): 30× Sales Enterprise as base + 30× Customer Service Enterprise as attach. 30 × ($95 + $20) = $3,450/month.

Savings: $2,250 per month. $27,000 per year. Without anything changing in functionality — Microsoft explicitly says base and attach are technically identical.

We saw this case last summer at a wholesaler from the Rhine-Main region. The customer had paid the full price for three years because their previous reseller had not adjusted the setup. Three weeks of re-provisioning — and from then on the renewals ran at the reduced price.

Example 2: Business Central Premium as base — the special rule

Microsoft has documented a remarkable exception in the Licensing Guide. Business Central Premium costs $100/user/month — lower than Sales Enterprise, lower than Customer Service Enterprise, significantly lower than Finance. A user with BC Premium and Sales Enterprise should normally take Sales Enterprise as base (highest price = base) and BC Premium as attach.

But: The Microsoft rule explicitly says (Licensing Guide p. 6, footnote):

"Users who license Business Central Premium as their base license ($100 user/month, billed annually) are eligible to add Customer Service Enterprise, Field Service or Sales Enterprise at the $20 user/month, billed annually attach price."

That is a Microsoft-specific concession for Business Central customers who additionally want to use CE modules. In practice: anyone with 25 BC Premium users and 10 of them also needing Sales Enterprise pays not $95 per Sales license, but $20 — although Sales is technically more expensive than BC Premium.

Calculation for 25 BC users with 10 Sales add-ons:

Standard logic: 25× BC Premium ($100) + 10× Sales Enterprise ($95) = $2,500 + $950 = $3,450/month
BC Premium special rule: 25× BC Premium ($100) + 10× Sales Enterprise as attach ($20) = $2,500 + $200 = $2,700/month

Difference: USD 750 per month, USD 9,000 per year. Significant for a company with 25 employees. We consider this one of the underrated concessions in the Microsoft Dynamics 365 model — precisely because many advisors apply the standard base-attach logic without knowing this exception.

When Base + Attach doesn't work

Three pitfalls we see repeatedly:

1. Mixed deployments — Enterprise and Professional not in the same environment

Microsoft does not allow mixing Sales Enterprise and Sales Professional in the same tenant environment (Licensing Guide p. 5, mixed deployments note). So anyone who wants to license some sales reps with Professional and others with Enterprise has to set up separate environments — which means technical and organizational effort.

2. Attach only works if the base exists

Microsoft writes: "Attach licenses may only be assigned to users with an appropriate qualifying base license." (p. 6). The system administrator cannot assign an attach license if the base is missing — Microsoft validates this automatically in the admin center. But: if the base license is later removed or canceled, the attach entitlement also drops. We saw this once at a customer who accidentally reduced their Sales Enterprise licenses — the Customer Service attach licenses became invalid, and in the next audit it was a problem.

3. Customer Insights is a special case

Customer Insights breaks the standard logic. Microsoft explicitly says: "Customer Insights attach licenses include the same default capacity entitlements as the Customer Insights base license." (p. 6, note).

Translated: while other attach licenses bring no additional capacity entitlements (they share the base's), a Customer Insights attach license gets its full own profile capacity. That is relevant if you need multiple Customer Insights instances — one per brand family, for example. Attach helps more here than elsewhere.

What we do when a customer comes to us with the wrong setup

Three steps, in this order:

Pull the license inventory. Microsoft 365 admin center → Billing → Licenses. Excel export. We match which users have which licenses — and which should be linked.
Run through the License Cost Calculator. Our License Cost Calculator calculates the optimization with Base + Attach automatically. We run the constellation through and compare actual vs. target.
Initiate re-provisioning with the reseller. If the customer is in the CSP model, that runs via us. If they're with another reseller or in the Enterprise Agreement, we do the preparation and hand over the proposal to the Microsoft account manager.

Effort for a typical license optimization: 6 to 10 hours of advisory, plus 2 to 4 weeks of waiting for the next renewal period. The savings are in most cases six figures over three years — that amortizes the advisory in the first quarterly bill.

If you are unsure whether your setup uses Base + Attach correctly: a 30-minute initial conversation with license inventory attached is typically enough for a first diagnosis. More about our offering on the licensing, pricing & cost page.

30-min initial conversation · free

Have your license setup checked for Base + Attach?

Send us a license inventory — we'll tell you in 30 minutes whether there is optimization room and on what order of magnitude.

Book appointment License Cost Calculator

Four more articles from this licensing set.

May 8, 2026 · Licensing