Your Microsoft 365 licence quietly includes a pool of SharePoint storage. Cross the line and the meter starts — and the SharePoint storage cost above that line is one of the most expensive per-gigabyte rates in your entire cloud stack. This is the complete 2026 pricing breakdown: what your licence actually includes, what Microsoft charges for every gigabyte past it, the annual bill at 1, 5, and 10 TB over quota, and what the exact same terabyte of cold data would cost if it lived in object storage instead. No vendor spin — just the numbers, with sources.
What’s included in your licence
SharePoint storage in Microsoft 365 is pooled at the tenant level, and the size of the pool is driven by how many licences you hold. The widely-cited formula is 1 TB of base storage plus 10 GB per licensed user. A 300-seat tenant, then, gets roughly 1 TB + 3 TB = 4 TB in the shared pool. Microsoft’s own documentation confirms the storage “is based on the number of licenses you have” and that all sites draw from one central pool, with individual sites capped at 25 TB (25,600 GB) each.
Two things make the pool fill faster than anyone budgets for. First, everything counts against it — documents, but also version history (every saved version is a full copy on many libraries), the two-stage recycle bin, and the SharePoint sites that back every Teams channel. Second, the pool is shared: one department’s runaway site collection eats headroom for the whole tenant. Most organisations don’t discover the ceiling until an admin gets the “storage is almost full” banner — at which point the only fast options all cost money.
Work a quick example. A 500-seat tenant pools 1 TB + (500 × 10 GB) ≈ 5.9 TB. That sounds generous until you remember it covers every SharePoint site, every Teams channel’s document library, and every retained version across the organisation. A handful of active project sites with rich media, plus years of accumulated version history, and a mid-size business is over the line inside a couple of years of normal use — without anyone doing anything wrong. From that point on, every additional gigabyte is billed at the overage rate below.
The Office 365 Extra File Storage add-on, priced out
Once you’re over the pool, Microsoft’s traditional answer is the Office 365 Extra File Storage add-on. You buy it in 1-GB increments from the Microsoft 365 admin center — though if you bought your subscription through Volume Licensing or a Cloud Solution Provider, you can’t purchase it directly from Microsoft and have to go through your partner.
The list price commonly quoted for the add-on is US$0.20 per GB per month. Microsoft doesn’t publish a single global number on the buy page because the exact rate varies by region, currency, and purchase channel — so treat US$0.20/GB as the reference figure and confirm your own tenant’s rate at checkout. At that reference rate, a single terabyte of overage is 1,024 GB × US$0.20 = about US$205 a month, or roughly A$290/TB/month once you convert and add GST. That is the number to hold every other option up against.
There is also a newer route: as of June 2026, Microsoft’s pay-as-you-go SharePoint storage is in public preview, metering overage through an Azure subscription instead of a fixed add-on. It changes how you’re billed, not the underlying economics — the data is still hot storage inside Microsoft’s walls, priced accordingly.
Annual SharePoint storage cost at 1, 5, and 10 TB over quota
The per-gigabyte rate feels small until you annualise it. Here’s the SharePoint storage cost of the Extra File Storage add-on at the US$0.20/GB/month reference rate, for three realistic amounts of overage:
- 1 TB over quota: ~US$205/month → ~US$2,460/year (≈ A$3,700).
- 5 TB over quota: ~US$1,024/month → ~US$12,290/year (≈ A$18,600).
- 10 TB over quota: ~US$2,048/month → ~US$24,580/year (≈ A$37,200).
And this only ever grows. Corporate data doesn’t shrink — it compounds — so today’s 5 TB of overage is next year’s 8 TB. The add-on is a recurring, escalating line item on a base of files that, in most tenants, are overwhelmingly cold: aged documents nobody has opened in a year or more. You can put your own numbers through the SharePoint storage cost calculator to see where your tenant lands.
What the same terabyte costs in object storage
Here’s where the gap becomes absurd. The cold files driving your overage don’t need premium, instantly-editable SharePoint storage — they need to be kept, findable, and restorable. That is exactly what S3-compatible object storage is for, and it’s priced in a different universe:
- Wasabi charges US$7.99 per TB per month (about US$0.008/GB) with no fees for egress or API requests on its pay-as-you-go plan.
- Backblaze B2 lists at roughly US$6 per TB per month (US$0.006/GB), with free egress up to three times your stored volume each month.
Sit that beside the Microsoft add-on and the ratio is stark: US$0.20/GB versus about US$0.006–0.008/GB — object storage is on the order of 25 times cheaper per gigabyte for the same bytes. Even Microsoft’s own cold tier, Microsoft 365 Archive at US$0.05/GB/month, sits well above raw object storage while keeping your data locked inside the tenant. We compared the two in detail in Microsoft 365 Archive vs third-party archiving.
The honest framing: object storage buys that price by trading instant, in-place editing for a retrieve-then-open step, and some providers attach terms worth reading — Wasabi, for instance, has a minimum-storage-duration policy on deleted objects. None of that matters for genuinely cold data, which is exactly the point: you don’t move your live document libraries to a bucket, you move the aged files that are quietly inflating the bill and leave everything hot where it is.
Cutting the SharePoint storage bill without deleting anything
The instinct when the banner appears is to delete — trim versions, empty recycle bins, hunt for duplicates. Those clean-ups help for a quarter, then the pool fills again, because the underlying problem isn’t mess; it’s that cold data is being stored on hot infrastructure. The durable fix is to move the cold slice off SharePoint to object storage, leave a stub link so nothing breaks for users, and stop the overage meter entirely — no files deleted, no links lost.
That’s ArchiveBridge’s whole job. Cold files are copied to a bucket, verified byte-for-byte with SHA-256 before the original is removed, and replaced with a stub that restores on one click. The cost swaps a ~A$290/TB/month Microsoft rate for A$29/TB/month management with your own bucket(storage billed directly by Wasabi or B2 at the list prices above), or A$49/TB/month all-in if we host the storage. On 5 TB of cold data, that’s the difference between roughly A$18,600 a year and a low four-figure sum — the same files, still searchable, still one click from restore.
The honest caveat: object-storage archiving means another vendor and an admin consent to manage, and the data physically leaves SharePoint’s native compliance boundary (a well-built tool stays Purview- and legal-hold-aware to compensate). If your overage is tiny and shrinking, Microsoft’s built-in tier may be simpler. If cold data is a large, growing line on your bill, the maths tilts hard toward moving it.
Either way, the decision runs on your numbers, not a rule of thumb. The fastest way to get them is a free, read-only tenant scan: it reports exactly how many gigabytes of aged files you’re paying the premium rate to keep, and what moving them would save — before a single file moves.