Coût du stockage Microsoft 365 en 2026 : ce qui change

On July 1, 2026, Microsoft raises prices across its enterprise plans. E3 moves from $36 to $39 per user per month. E5 moves from $57 to $60. At the same time, Microsoft launched a new pay-as-you-go billing model for SharePoint Online storage in June 2026.

For a CIO or CFO managing between 500 and 5,000 licensed users, these two changes point in the same direction: a predictable, structural cost increase that compounds with every gigabyte of data your organization accumulates. Understanding how storage billing actually works, before your next contract renewal, gives you the leverage to act on it.

What Your Microsoft 365 Subscription Actually Includes for SharePoint Storage

Microsoft publishes the SharePoint storage quota formula directly in its Learn documentation (Microsoft, SharePoint Limits Service Description, 2025): 1 TB base storage per tenant, plus 10 GB per eligible licensed user. That capacity is pooled across all SharePoint sites in the tenant, including Teams-connected sites.

For 500 E3 users, your total available quota is 6 TB (1 TB + 500 x 10 GB). For 1,000 users, it reaches 11 TB. Not every license contributes: F1 licenses and certain Frontline plans do not add to the pooled quota, even if those users are active in the tenant.

OneDrive storage is separate. Each user has an individual quota (1 TB per user on most E3, E5, and Business Standard plans) that sits outside the SharePoint pooled total above.

One frequently overlooked factor: OneDrive accounts belonging to former employees with no active license continue consuming SharePoint pooled quota, even after those users have left the organization (Microsoft Learn, Manage unlicensed OneDrive user accounts). In organizations with significant headcount turnover, this can represent years of accumulated storage that never appears in standard usage reports.

Storage volumes also grow faster than most IT budgets account for. According to IDECSI observations across their enterprise client base (Webinar: Microsoft 365 Storage Management, 2024), M365 data volumes grow at 30 to 40 percent per year, a trend that accelerates with generative AI adoption. A tenant at 80 percent of its quota today can expect to exceed it within 12 to 18 months without corrective action.

One thing worth knowing: when a tenant exceeds its SharePoint quota, the default behavior is read-only mode, blocked uploads, and suspended site creation. This is existing behavior, not new policy. Its impact grows as data volumes increase. Microsoft now offers an alternative to that lockout: the pay-as-you-go billing model (MC1330893), covered in the next section.

Per Microsoft's published documentation, every non-education Microsoft 365 tenant receives 1 TB of base pooled SharePoint storage plus 10 GB per eligible licensed user, shared across all sites and Teams workspaces in the organization (Microsoft Learn, 2025).

The Real Cost of a Storage Overage in 2026

When a tenant exceeds its included quota, two options are available: purchase the Office 365 Extra File Storage add-on or enable the new pay-as-you-go billing model. The per-GB rate is the same for both: $0.20 per GB per month. That is $200 per TB per month, or $2,400 per TB per year (Microsoft admin center, 2026).

To make this concrete, here is an illustrative example. A 500-user E3 organization with 10 TB of current SharePoint consumption exceeds its included quota by 4 TB (10 TB used minus 6 TB included). At $0.20 per GB per month, that overage costs $9,600 per year (4 TB x $2,400 per TB per year).

The formula applies to any tenant size: annual overage cost = (actual consumption in TB - included quota in TB) x $2,400

The July 1, 2026 license increase is a separate budget line: $3 more per E3 user per month, or $18,000 per year for a 500-user organization. These two costs are distinct in nature. The license increase applies to every E3 tenant regardless of storage usage. The storage overage cost depends entirely on how much data your organization has accumulated. That distinction matters: the license increase is fixed, the storage cost is actionable.

Before buying additional storage, one lower-cost option is worth evaluating: Microsoft 365 Archive meters archived SharePoint content at $0.05 per GB per month, a 75% reduction compared to the standard $0.20 overage rate (Microsoft Learn, archive-pricing, 2026). Archive is not deletion. Content stays searchable and reactivatable. For data that must be retained for compliance or legal reasons but is rarely accessed, Archive can materially reduce effective overage costs. Example: archiving 3 TB of inactive content instead of paying standard overage reduces that line from $7,200 to $1,800 per year.

Storage overage is billed at $2,400 per TB per year. That formula applies directly to your tenant's actual consumption. It is the only M365 cost line in 2026 where action can still change the outcome.

SharePoint Pay-as-You-Go Billing: What Changes, What Stays the Same

Microsoft put SharePoint Online pay-as-you-go storage into public preview in June 2026 (Microsoft Learn, commerce/add-storage-space, 2026). The model is opt-in, not automatic. Enabling it requires connecting an Azure subscription and manually configuring a billing policy in the Microsoft 365 admin center.

Without pay-as-you-go enabled, default behavior when quota is exceeded remains unchanged: the tenant enters read-only mode, uploads are blocked, and new site creation is suspended. With it enabled, billing starts automatically for any storage consumed above the included quota, but quota-related alerts are disabled and cost reporting carries a 24-hour delay.

Note for US public sector and regulated environments: pay-as-you-go SharePoint storage is not available for GCC or GCC High tenants in the current preview (Microsoft Learn, 2026). Organizations in those environments must continue using the Office 365 Extra File Storage add-on to manage overages. General availability is expected in September 2026 for eligible commercial tenants.

Starting in July 2026, Microsoft is also rolling out pay-as-you-go billing for OneDrive storage in public preview, for commercial tenants outside the education sector and GCC environments. Organizations enabling both models can eliminate read-only blocking risks, but need an Azure cost monitoring strategy to avoid uncapped charges.

Enabling pay-as-you-go SharePoint storage eliminates the risk of read-only lockouts, but it disables quota alerts and creates uncapped automatic billing, making proactive data volume monitoring a requirement rather than a best practice.

The Biggest Cost Lever You're Likely Overlooking: Stale Data

Before purchasing additional storage or enabling pay-as-you-go, finance and IT leaders should ask a more fundamental question: how much of what is currently stored in your M365 tenant is actually in use?

According to IDECSI observations presented in their Microsoft 365 Storage Management webinar (2024) and confirmed across their enterprise client base, 25 to 50 percent of data stored in a Microsoft 365 tenant is stale or duplicated: redundant file copies, outdated document versions, Teams workspaces from completed projects, data from former employees still consuming quota. On a tenant running at 10 TB of consumption, that represents 2.5 to 5 TB of recoverable capacity.

Returning to the illustrative example: a 500-user E3 organization consuming 10 TB with a 4 TB overage can eliminate 2 TB of stale data, cutting its annual overage cost from $9,600 to $4,800 (2 TB x $2,400), with no new licenses and no infrastructure changes.

This lever is actionable. According to the IFOP/IDECSI study (2024), 85 percent of employees say they are willing to adopt a routine of deleting unneeded files, provided they have the right tools to do it. The obstacle is not behavior. It is visibility: employees do not have a personal view of their own data in M365, so they cannot act on what they cannot see.

For organizations in regulated industries (HIPAA, CMMC, financial services), a cleanup initiative requires a compliance review before deletion. Not all stale data can be removed without verifying retention obligations. The structured approach matters: inventory first, classify by retention policy, then remediate. The IDECSI methodology covers this sequencing explicitly.

The Copilot angle adds urgency here. Microsoft Copilot accesses everything a user is permitted to access. Stale, overshared data sitting in your tenant is not just a storage cost: it becomes a security exposure the moment Copilot can surface it. IDECSI covers the security risks introduced by Microsoft 365 Copilot in a dedicated article.

On a Microsoft 365 tenant over its SharePoint quota, stale and redundant data is the primary cost lever: every terabyte recovered saves $2,400 per year in overage charges, with no additional infrastructure and no IT overhead.

Reclaim Control in Under 4 Weeks with My Data Management

My Data Management is the IDECSI solution designed to turn a storage cartography into concrete action, without adding workload to your IT team. The process runs in three sequential steps.

The diagnostic phase maps your entire M365 storage footprint through Power BI dashboards: highest-consumption sites, dormant content, volumes by department and content type. This mapping is produced in one to two weeks and becomes the decision foundation for all cleanup actions that follow.

The cleanup phase puts users in the driver's seat. Each employee gets access to an intuitive interface that shows their own stale data and lets them delete it in a few clicks, without IT involvement at the file level. IT orchestrates and monitors the campaign. Users own the remediation decisions on their own content. That is the shared accountability model that makes results stick.

Gains are tracked in real time through a ROI dashboard. Deleted volumes, avoided storage costs, and progress toward reduction targets are visible at every stage of the program.

Results from current clients: SUEZ deleted 110 TB of data (23 percent of their total M365 footprint) in 10 weeks. Cergy-Pontoise Agglomeration eliminated 1,796 sharing risks in the first campaign, removing 50 percent of identified risks, and 70 percent by the second campaign.

For organizations that want to go deeper on SharePoint storage governance and quota management, the technical methodology is covered in the IDECSI guide to Microsoft 365 storage optimization.

My Data Management reduces M365 storage consumption without adding IT overhead, by activating user-level accountability for data cleanup. Programs deliver measurable ROI within four weeks, tracked in real time through a dedicated dashboard.