Microsoft Sentinel Cost, Plus Defender: More Expensive Than You Think
Many organizations assume that because they already pay for Microsoft 365 licensing, adding Sentinel as their SIEM is essentially free or cheap. This assumption is dangerously wrong. When you add up ingestion costs, data retention, and the Defender license tier needed to actually get value from Sentinel, the total cost of ownership is significantly higher than most expect — and often more expensive than outsourcing to a managed SOC entirely.
Key Assumptions
To make this analysis concrete, we are modeling a mid-market organization with the following profile:
- 350 employees with Microsoft 365 E3 licenses
- 5 offices — 4 branch locations and 1 headquarters
- 6 firewalls across all sites
- A mix of remote and on-premises workers
- Limited in-house security staff — no dedicated SOC team
This is a common profile for organizations evaluating Sentinel. They have enough infrastructure to generate meaningful log volumes, but not enough headcount to build a security operations center from scratch.
Sentinel Pricing
Microsoft Sentinel pricing is consumption-based, meaning you pay for every gigabyte of data ingested per day. There are two primary pricing models:
- Pay-as-you-go: $5.22 per GB/day
- 100 GB/day commitment tier: $3.43 per GB/day
For our modeled organization, here is what daily log volumes look like:
| Log Source | Count | Daily Volume |
|---|---|---|
| Windows Endpoints | 350 | 716.8 MB |
| Network Firewall | 6 | 18.0 GB |
| EDR Agents | 350 | 3.8 GB |
| Total | ~22.5 GB/day |
With those volumes, the monthly cost breakdown looks like this:
| Cost Component | Monthly Cost |
|---|---|
| Sentinel + Log Ingestion | $2,955.00 |
| Data Retention (9 months interactive) | $629.63 |
| Data Retention (12 months archive) | $167.90 |
| Combined Sentinel Cost | $3,752.63/month |
Defender License Costs
Sentinel on its own is just a SIEM — a log aggregation and analytics platform. To get endpoint detection, automated investigation, and meaningful alert context, you need Microsoft Defender. Defender comes in several tiers, all priced per user per month:
| License Tier | Per User/Month | Monthly (350 users) | Annual (350 users) |
|---|---|---|---|
| Defender Plan 2 Add-on | $5.00 | $1,750.00 | $21,000.00 |
| E5 Security | $12.00 | $4,200.00 | $48,000.00 |
| Enterprise Mobility E5 | $16.40 | $5,740.00 | $68,880.00 |
| Full E5 | $31.00 | $10,850.00 | $130,200.00 |
Total Cost of Ownership
Using the most conservative Defender tier (Plan 2 Add-on at $5/user/month) combined with Sentinel costs, the baseline total comes to:
- Monthly: $5,502.53 ($3,752.63 Sentinel + $1,750.00 Defender)
- Annual: $66,030.36
That is the floor. If your organization needs the richer capabilities in E5 Security or Full E5 licensing, annual costs jump to $93,631 or $175,831 respectively — and that is before you account for the staff to actually operate, tune, and respond to alerts in the platform.
Managed SOC Comparison
A managed SOC — where a third party provides the SIEM, EDR, 24/7 monitoring, threat hunting, and incident response — typically runs $4,000 to $7,000 per month all-inclusive for an organization of this size. That price includes the technology stack, the analyst team, and ongoing tuning. There is no additional licensing to buy, no retention fees, and no headcount to hire.
When Sentinel Makes Sense
Sentinel is a strong platform for organizations that:
- Already have E5 licensing for other reasons (compliance, telephony, etc.)
- Have a dedicated security team capable of writing KQL queries, tuning detections, and running investigations
- Need deep integration with Azure-native workloads
- Have the budget for both the platform and the people to operate it
When to Avoid It
If your organization has limited security staff, is running E3 licensing, and is evaluating Sentinel primarily because it is a Microsoft product, you are likely better served by a managed SOC. The total cost will be comparable or lower, and you will get 24/7 coverage without hiring a team to run the platform.