What 50 Microsoft 365 users really cost over three years: Business Premium vs E3 (plus add-ons)

Prices and rules checked 1 November 2026 (2026-11-01). The prices are Microsoft list prices for an annual commitment, excluding tax, and your reseller's price will differ. Every figure is calculated from them by script and re-added by hand. This is a Microsoft 365 licensing cost model, not a quote.

The decision and the finding

The question. A company with 50 users must pick a plan for the next three years: Microsoft 365 Business Premium or Microsoft 365 E3. If E3 is chosen, what has to be added to bring its security close to what Business Premium already includes, and what does that cost?

The finding, at list price for 50 users over 36 months:

• Business Premium: $39,600 (INR 3,294,000). E3: $70,200 (INR 5,841,000). E3 costs $30,600 (INR 2,547,000) more, which is $17 (INR 1,415) per user per month.
• E3 does not include two security products that Business Premium does: Defender for Business (endpoint detection and response) and Defender for Office 365 Plan 1 (Safe Links, Safe Attachments, impersonation protection). Adding them at US list prices of $3 and $2 brings the E3 stack to $44 per user per month, exactly double Business Premium. Over three years that is $79,200, a gap of $39,600.
• Mailbox size is not a reason to pay for E3. Microsoft's Exchange Online limits page lists the same 100 GB mailbox and 1.5 TB auto-expanding archive for Business Premium and E3.
• Discounts do not close the gap. E3 alone would need to be 43.6 percent below list to match Business Premium, and the E3 stack with both add-ons would need 50 percent, far beyond the 5 to 20 percent tested below.
• The user count does not change which plan is cheaper. The price ratio is a constant 1.77 to 1 whether you have 10 users or 300; the user count only scales the stakes. What does change the decision is the 300-user cap on the Business plans, a specific right only E3 gives, or a mix of both plans.

An opinion the numbers support. Treat E3 as a feature purchase, not a price purchase. Default to Business Premium for up to 300 users. Buy E3 for the named people who need something it has and Business Premium lacks, and do not assume the whole company must move together: Microsoft allows Business and Enterprise plans in the same account. Ten of your 50 users on E3 and 40 on Business Premium costs $45,720 over three years, $6,120 more than all Business Premium and $24,480 less than all E3.

Prices used (retrieved 2026-11-01)

Assumptions that are not prices: 50 users who all need the same stack, the editions with Teams, a 36-month horizon with flat prices (price rises are tested below), and no partner or agreement discount (tested below). Where this site's Microsoft 365 licence cost calculator shows the same prices, it takes them from the same data file.

What is the same and what differs

I checked the features that decide this on Microsoft Learn pages, listed under Sources.

Two things follow. First, the "Plan 1" label on Business Premium's Exchange does not mean a smaller mailbox. Second, the real security difference is narrow: endpoint detection and response, and Safe Links and Safe Attachments. Those are exactly what the add-ons below price.

The calculation, step by step

The model is a multiplication. For a stack priced at P per user per month, with U users, over three years:

yearly cost      = P x U x 12
three-year cost  = yearly cost x 3          (prices flat, annual commitment)
with a price rise r at each renewal:
three-year cost  = yearly cost x (1 + (1 + r) + (1 + r)^2)

Worked for 50 users in US dollars, and again in rupees where Microsoft publishes the price:

Business Premium     22 x 50 x 12 = 13,200 a year    x 3 = 39,600
                     1,830 x 50 x 12 = 1,098,000     x 3 = 3,294,000 (INR)
E3                   39 x 50 x 12 = 23,400 a year    x 3 = 70,200
                     3,245 x 50 x 12 = 1,947,000     x 3 = 5,841,000 (INR)
E3 + Defender for Business (39 + 3 = 42)
                     42 x 50 x 12 = 25,200 a year    x 3 = 75,600
                     3,495 x 50 x 12 = 2,097,000     x 3 = 6,291,000 (INR)
E3 + Defender for Business + Defender for Office 365 P1 (39 + 3 + 2 = 44)
                     44 x 50 x 12 = 26,400 a year    x 3 = 79,200
E3 + Defender Suite (39 + 12 = 51)
                     51 x 50 x 12 = 30,600 a year    x 3 = 91,800

The script that produced these numbers is published with the site code (docs/cost-models/m365-three-year.mjs) and run under JavaScriptCore.

Results

The like-for-like row is the fourth: E3 plus the two add-ons approximates Business Premium's email and endpoint security, and it costs twice as much.

Sensitivity: what changes the answer

User count. The gap scales in a straight line with users. The ratio never moves.

The 300-user cap. Business Premium is limited to 300 provisioned licences across the Business family. Above 300 you need E3 (or another Enterprise plan) for the excess. For 320 users, 300 on Business Premium and 20 on E3 costs $265,680 over three years; all 320 on E3 costs $449,280.

Price rises at renewal. Microsoft can change prices at renewal; this table is a what-if, not a forecast.

Discounts. A discount on E3 narrows the gap slowly, because the starting gap is large.

A mixed fleet. Because the plans can coexist, buy E3 only for the people who need it.

Add-ons. Add-ons that cost the same on both plans (for example Microsoft Teams Phone Standard at $10 a user) leave the dollar gap untouched but shrink the percentage: with $10 added to both, the ratio falls from 1.77 to 1.53. Copilot is the one add-on whose price may differ by plan. For 10 of your 50 users, Copilot Business at $21 costs $7,560 over three years (INR 628,200), and the enterprise Copilot at $30 costs $10,800 (INR 898,200), a difference of $3,240. I could not verify whether Copilot Business can be attached to E3 users, so ask: if it can, the difference vanishes; if only the enterprise price applies, E3 costs you that much more per Copilot user.

Where this model is wrong or does not apply

• List prices are not your prices. Cloud Solution Provider and Enterprise Agreement discounts, promotions and currency differences change both columns. Treat the model as a way to see the shape, then redo it with your quote.
• It assumes every user gets the same stack. Frontline staff, shared mailboxes and external contractors often need cheaper licences, which this model ignores.
• Business Standard is not modelled. It costs $14 (INR 860) but includes Entra ID Free, not Plan 1, and no Intune Plan 1 or Defender for Business; adding those later is a different calculation.
• The add-on route is unconfirmed. I did not verify that Defender for Business, a standalone product for businesses of up to 300 employees, can be assigned to E3 users in your tenant. Your reseller can confirm.
• Admin time is not priced. Neither stack removes the work of configuring Conditional Access, Intune and Defender. Migration effort, training and any third-party tools are outside the model.
• The Windows and eDiscovery rows are unresolved. If you need Windows Enterprise features or eDiscovery cases, those two rows could justify E3 for specific users.
• Teams. The with-Teams editions are used. Microsoft also sells editions without Teams, with different prices, and in some regions Teams is sold separately.
• Billing term. The prices are for an annual commitment paid yearly. Monthly billing may cost more; I did not verify the premium.
• India. INR prices exclude GST. I did not retrieve INR prices for Defender for Office 365 or the Defender Suite, so those rows say "enter your quote".

Decision checklist

• Are we at or under 300 users, now and in three years?
• Which named users need something Business Premium lacks (Windows Enterprise features, eDiscovery, anything else on a written requirement)? Buy E3 for those people only.
• Do we need endpoint detection and response, and Safe Links and Safe Attachments? If yes and we are on E3, price the add-ons before comparing.
• What discount does our agreement actually give, on both plans, in writing?
• Have we priced a 5 or 10 percent rise at renewal into the three-year view?
• Are Copilot or other add-ons planned, and are they available on both plans at the price we assume?
• Who will configure and run Conditional Access, Intune and Defender, and is that time budgeted?

Questions to ask your reseller or Microsoft

• What is the exact price per user per month for Business Premium, E3 and each add-on under our agreement, in our currency, with and without tax?
• Can Defender for Business and Defender for Office 365 Plan 1 be assigned to E3 users, and is there a user cap?
• Is eDiscovery (standard) included in Business Premium? Which Windows rights come with each plan?
• Can Copilot Business be added to E3 users, or do we need the enterprise Copilot?
• What happens to price at renewal, and is the price fixed for the commitment term?
• What does monthly billing cost compared with annual billing?
• If we grow beyond 300 users, how do we move users between plans without disruption?

Related reading and tools

Check your own seat counts and prices in the Microsoft 365 licence cost calculator, review who is using what with the licence audit guide, and see the server side of the same budget in the three-year model for a 20-VM small business and the Windows Server licensing calculator.

How we calculated

Three-year cost = price per user per month x users x 12 x 3, with a renewal rise r applied as x (1 + (1 + r) + (1 + r)^2). Stack prices are sums of per-user list prices. Plan and add-on prices for Business Premium, E3, Defender for Business and Copilot come from Microsoft's pages through this site's price data file (checked 2026-11-01); the Defender for Office 365 Plan 1 and Defender Suite prices were read from Microsoft's security pricing pages the same day. Every number was computed by script under JavaScriptCore and re-added by hand. Feature statements were checked on Microsoft Learn on 2026-11-01.

Sources

Prices and rules checked 1 November 2026.

• Microsoft 365 business plans and pricing (with Teams) (Business Premium, Defender for Business, Copilot Business)
• Microsoft 365 enterprise plans and pricing (E3, Microsoft 365 Copilot)
• Microsoft 365 security pricing for business (Defender for Office 365 Plan 1)
• Microsoft security pricing overview (Defender Suite)
• Microsoft 365 and Office 365 plan options (300-user limit, mixing plans, plan contents)
• Microsoft 365 for business security overview (Entra ID P1, Intune Plan 1, Defender for Business, Defender for Office 365 Plan 1)
• Microsoft Defender service description (Defender for Endpoint Plan 1 in E3, Defender for Business)
• Microsoft Purview service description (DLP, retention, labels, eDiscovery)
• Exchange Online limits (mailbox and archive sizes)
• Microsoft Product Terms for Microsoft 365 (E3 contents)
• Microsoft 365 licence cost calculator and licence audit guide