CDN vs Origin Bandwidth Cost Calculator
Why CDN economics matter
Content delivery networks (CDNs) promise faster pages and lower bandwidth bills by caching assets closer to users. Yet the contract math can be daunting. Providers blend per-gigabyte transfer charges, request fees, commit minimums, and overage penalties. Meanwhile, your origin infrastructure still handles cache misses, ingest traffic, and dynamic responses. This calculator brings transparency by comparing monthly spend with and without a CDN using your actual traffic profile. It also estimates payback on one-time onboarding costs and captures how growth amplifies savings over time.
The tool is useful for engineering leaders negotiating CDN renewals, finance teams modeling total cost of ownership, and founders planning to expand into new regions. Enter monthly transfer volumes, cache hit expectations, request counts, and pricing terms. The output shows baseline origin costs, projected CDN invoices, residual origin spend, and blended totals. A payback calculation highlights how many months of savings are required to offset onboarding or migration expenses. To keep the analysis grounded in reality, you can note expected latency improvements, reminding stakeholders that performance gains complement cost savings.
How the calculations work
The model converts monthly data transfer from terabytes to gigabytes using binary multiples (1 TB = 1,024 GB) so the cost math matches typical provider billing. Cache hit ratio determines what share of traffic the CDN serves. Cache hits incur CDN transfer fees but spare the origin from outbound bandwidth. Cache misses still traverse the CDN, often incurring transfer charges, yet they also hit the origin, which pays its own egress rate. For simplicity, this calculator assumes your CDN charges the same rate for hits and misses, a common scenario for flat-rate contracts. If your vendor bills origin shield traffic separately, adjust the cache hit ratio downward to reflect the extra origin load.
Monthly costs break down as follows:
In this expression, \(S\) represents CDN spend, \(G\) is total gigabytes transferred, \(P\) is the per-GB price, \(R\) is request volume in millions, and \(F\) is the fee per million requests. Origin spend without a CDN equals \(G \times O\), where \(O\) is the origin price per gigabyte. After deploying a CDN, origin spend shrinks to \(G \times (1 - H) \times O\), with \(H\) denoting cache hit ratio. The calculator then adds any contract minimums to CDN spend and compares the combined total against the baseline origin cost.
Worked example
Consider a video platform pushing 120 TB of data per month with 950 million requests. Origin egress from its cloud provider costs $0.09/GB. A CDN vendor offers $0.035/GB transfer, $0.75 per million requests, and a $4,000 monthly commit. The engineering team expects a 78% cache hit ratio after tuning cache-control headers. Implementing the CDN requires $15,000 in onboarding work—configuration, TLS provisioning, load testing, and observability integration. Management also wants to note an expected 45 ms latency improvement for marketing and user experience teams.
Feeding these numbers into the calculator shows baseline origin spend of about $11,059 per month. With the CDN, transfer charges land near $4,300 (120 TB × 1,024 × $0.035), request fees add $713, and the $4,000 commit brings CDN spend to $9,013. Origin costs fall to $2,432 because only 22% of traffic now leaves the origin. Total blended spend becomes $11,445—slightly higher than the origin-only baseline. However, once traffic grows 20% annually, year-two monthly traffic reaches 144 TB, pushing origin-only costs to $13,271. CDN savings widen because the commit spreads over more volume, yielding $12,021 in blended spend. Payback on the onboarding cost occurs after roughly 34 months when cumulative savings surpass the initial outlay.
Interpreting the comparison table
| Scenario | Monthly cost | Origin bandwidth | Latency impact |
|---|---|---|---|
| Origin only | $11,059 | 100% | Baseline |
| CDN deployed | $11,445 | 22% | -45 ms |
| Year 2 with growth | $12,021 | 22% | -45 ms |
The table indicates that even when initial costs rise modestly, performance improvements may justify the investment. As traffic grows, CDN economics often improve because commit minimums are amortized across more gigabytes. You can adjust the growth rate input to test when savings outpace the baseline. If the CDN remains more expensive even at higher traffic, it signals a need to renegotiate pricing, improve cache hit ratio, or consider multi-CDN strategies.
Latency and user experience considerations
While the calculator focuses on costs, latency improvements deserve equal attention. Faster load times reduce bounce rates, improve SEO rankings, and increase conversion. If marketing teams quantify the revenue uplift from a 45 ms improvement, you can add that value to the savings column when presenting to leadership. Some organizations treat latency as an opportunity cost; the calculator’s latency field provides a simple reminder to include qualitative benefits in decision memos.
Strategies to raise cache efficiency
Cache hit ratio is the lever you control most. Audit cache-control headers, leverage stale-while-revalidate directives, and minify assets to increase reuse. Use CDN logs to identify low-hit paths and adjust origin routing or caching rules accordingly. If dynamic content dominates, consider edge computing or partial caching to reduce origin load. Every percentage point increase in cache hits reduces origin egress cost while keeping CDN spend flat. Plug new hit ratios into the calculator to quantify savings for engineering sprints.
Payback and long-term planning
The payback metric divides onboarding cost by monthly savings. If monthly savings are negative, the calculator reports that payback is not achieved, prompting a rethink of vendor choice or configuration. When savings exist, you can project cumulative value by applying the growth rate input over a multi-year horizon. The model compounds traffic growth annually, recalculating both CDN and origin spend to show how savings evolve. Export the CSV for board presentations or vendor negotiations.
Some teams even track CDN cost per customer session to understand how onboarding new markets affects unit economics.
Negotiating smarter CDN contracts
Armed with the calculator’s outputs, you can negotiate from a position of strength. Share projected blended costs with vendors and ask them to model alternative rate cards—lower request fees, regional price breaks, or tiered commits that scale with traffic. Many providers offer trial periods where they waive onboarding costs; plug a zero into the setup field to see how that alters payback. If multi-CDN strategies are on the table, run the calculator for each contender and compare savings against the operational overhead of juggling multiple providers.
Security and edge compute add-ons, such as web application firewalls or serverless functions, can increase CDN invoices. Use the calculator to isolate core delivery costs, then layer on estimated prices for extras. Presenting a clean separation helps finance understand which expenses drive performance versus security posture. It also enables product teams to evaluate whether edge logic unlocks new revenue streams that offset the added spend.
Limitations and assumptions
The tool simplifies several complexities. It ignores tiered pricing, regional rate differences, and premium features like real-time logs or image optimization that carry extra fees. It also assumes CDN request fees apply uniformly; some providers include a quota before charging. Origin costs may include storage or compute beyond egress, which you should add manually if significant. Additionally, cache hit ratio can fluctuate daily; use conservative estimates or run multiple scenarios to bracket outcomes.
Despite these limitations, the CDN vs Origin Bandwidth Cost Calculator offers a structured way to evaluate delivery strategies. By grounding discussions in quantifiable assumptions, it helps teams balance performance goals with financial discipline.