Azure bandwidth and egress costs: how to estimate outbound data transfer

Bandwidth is a top source of surprise cloud bills. The core strategy is to split traffic into destinations and validate boundaries: internet egress, cross-region transfer, and origin egress to CDN.

Azure egress inputs

  • Destination zone: Zone 1/2/3 pricing tiers.
  • GB/month: baseline and peak transfer.
  • Free allowances: subtract any free tiers first.

1) Break down traffic by destination (define the boundary)

  • To the internet (end users, partners, third-party APIs, SaaS)
  • Cross-region (replication, multi-region services, DR)
  • To a CDN origin (cache fill, misses, revalidation)

Most budgeting mistakes are boundary mistakes: counting the same GB twice, or pricing the wrong path with a blended rate.

2) Estimate GB/month (pick the best method you can)

Method A: From billing exports (best for budgets)

  • Identify outbound transfer usage types and sum by month.
  • Break down by region and by service (one noisy service can dominate egress).

Method B: From throughput charts (good first pass)

  • Convert Mbps to GB/month with the Units Converter.
  • Apply a boundary share (internet vs cross-region vs CDN origin) and test low/medium/high sensitivity.

Method C: From requests and payload size

3) Apply an effective rate (for planning)

For budgeting, it is acceptable to use a blended effective rate per GB and refine later. The key is to avoid double-counting (for example, counting CDN edge bandwidth as origin egress).

Tool: Data egress cost calculator.

Worked estimate template (copy/paste)

  • Internet egress = GB/month delivered to end users (separate CDN bandwidth from origin egress)
  • CDN origin egress = cache misses/month * object size (GB) + revalidation traffic
  • Cross-region = replication GB/month + cross-region reads GB/month

Common pitfalls

  • Double-counting CDN bandwidth and origin egress as the same GB.
  • Mixing regions and applying one $/GB to multiple transfer paths.
  • Unit mistakes: GB vs GiB and Mbps vs MB/s.
  • Ignoring peak events (backfills, audits, incidents) that dominate a month.
  • Assuming all outbound is billed equally (internal vs internet vs cross-region differ).

How to validate

  • Reconcile your modeled GB/month boundaries against one real billing cycle.
  • Spot-check the top destinations/services to confirm the boundary mapping is correct.
  • Keep a separate peak scenario for backfills and incident windows.

Related tools

Egress Response transfer CDN bandwidth Network transfer costs

Sources

Related guides

Azure CDN pricing: estimate bandwidth, requests, and cache fill
A practical Azure CDN estimate: edge bandwidth, request volume, and origin egress (cache fill). Includes validation steps for hit rate, purge behavior, and big endpoints.
Azure Front Door pricing: model requests, bandwidth, and origin traffic
A practical Azure Front Door cost model: edge bandwidth, request volume, logging, and origin traffic (cache fill). Includes a checklist to validate hit rate and avoid double-counting egress.
Azure API Management pricing: model requests, transfer, and log volume
A practical API Management estimate: request volume, response transfer, and logs/observability. Includes a checklist to validate retries, payload size, and usage tiers.
Azure Cosmos DB pricing: a practical estimate (RU/s, storage, and egress)
A driver-based Cosmos DB estimate: RU/s capacity, stored GB, and data transfer. Includes a workflow to validate RU drivers and avoid underestimating burst, hot partitions, and retries.
Azure Event Hubs Pricing & Cost Guide (throughput, retention, egress)
Estimate Event Hubs cost from throughput units, ingress, capture/storage, and egress. Includes a planning checklist.
Azure Load Balancer pricing: L4 traffic and data processing model
A practical cost model for Azure Load Balancer: hours, data processed, and egress boundaries. Includes a workflow to estimate GB processed from RPS and payload size, plus a validation checklist for peaks and retries.

Related calculators

CDN Cost Calculator
Estimate total CDN cost from bandwidth and request pricing.
CDN Bandwidth Cost Calculator
Estimate monthly CDN bandwidth cost from GB transferred and $/GB pricing.
CDN Request Cost Calculator
Estimate CDN request fees from monthly requests and $ per 10k/1M pricing.
Data Egress Cost Calculator
Estimate monthly egress spend from GB transferred and $/GB pricing.
API Response Size Transfer Calculator
Estimate monthly transfer from request volume and average response size.
VPC Data Transfer Cost Calculator
Estimate data transfer spend from GB/month and $/GB assumptions.

FAQ

What usually drives egress cost?
Total outbound GB to the internet is usually the main driver, but cross-region and CDN origin egress can add large hidden lines.
How do I estimate quickly?
Estimate monthly outbound GB by destination and multiply by an effective blended rate for planning. Keep CDN edge bandwidth separate from origin egress.
How do I validate?
Validate real outbound GB from a representative window and verify which paths are billed (internal vs internet vs cross-region).
Last updated: 2026-02-07