API Rate Limit ↔ Cost Calculator
API gateway rate limit vs billing threshold — the gap is where cloud providers make margin. Your gateway enforces 1000 req/s. AWS bills per request. The price curve is not linear. Model per-request cost, data transfer egress, TLS termination, and burst overhead across AWS, GCP, Azure, and self-hosted (NGINX/Kong).
📐 API Traffic Profile
Set sustained req/s, avg payload size, burst ratio. The engine computes monthly volume, then maps to per-provider pricing — tiered volume discounts included. Self-hosted vs. managed: the crossover point may surprise you.
📋 Managed API Gateway Pricing Reference (US East)
Published list prices as of 2026. Actual costs vary with volume commitments, reserved capacity, and enterprise agreements.
| Provider / Tier | Per-Million Requests | Data Transfer ($/GB) | Free Tier / Notes |
|---|---|---|---|
| AWS REST API Gateway | $3.50 | $0.09 (internet) | 1M req/mo free × 12 months |
| AWS HTTP API Gateway | $1.00 | $0.09 (internet) | 1M req/mo free × 12 months |
| AWS WebSocket API | $1.00 /M msgs + $0.25 /M conn-mins | $0.09 (internet) | 1M msgs + 750K conn-mins free |
| GCP API Gateway | $3.00 | $0.12 (internet) | 2M req/mo free |
| GCP Apigee X (Enterprise) | $4.50+ | Included | Volume discounts at 100M+/mo |
| Azure API Management (Basic) | $3.00 | $0.087 (internet) | 1M req/mo included in tier |
| Azure API Management (Standard) | $2.00 | $0.087 (internet) | Includes developer portal |
| Azure API Management (Premium) | $1.20 | $0.087 (internet) | VNet injection, multi-region |
| Self NGINX / Kong on EC2 (c5.xlarge) | ~$0.07 | $0.09 (AWS internet) | ~$124/mo compute + egress only |
| Self HAProxy / Envoy (c5.2xlarge) | ~$0.04 | $0.09 (AWS internet) | ~$248/mo compute for HA pair |
API Rate Limiting Economics: Why "Free Tier" Math Breaks at Scale
API gateways charge per request — a pricing model that looks cheap at low volume but becomes a dominant infrastructure cost at scale. A service handling 1,000 requests per second processes ~2.6 billion requests per month. At AWS REST API Gateway pricing of $3.50 per million, that's over $9,000/month before data transfer. The same workload on a pair of self-hosted NGINX instances costs roughly $250/month in compute — a 36× cost difference.
How This Calculator Works
The engine converts your sustained rate limit (req/s) into monthly request volume using req/s × 86,400 × 30.4375 (mean days per month accounting for leap years). It then applies provider-specific pricing models:
| Provider | Per-Million Rate | Volume Discounts | Best For |
|---|---|---|---|
| AWS REST API Gateway | $3.50/M | None (flat rate) | AWS-native microservices with Lambda backends |
| AWS HTTP API Gateway | $1.00/M | None (flat rate) | Cost-sensitive HTTP proxies, no auth/transform needs |
| GCP API Gateway | $3.00/M | None; Apigee offers volume tiers | GCP Cloud Functions / Cloud Run backends |
| Azure API Management | $1.20–$3.00/M | Tier-based: higher tiers = lower per-call cost | .NET / Azure-native stacks with VNet requirements |
| Self-Hosted (NGINX/Kong) | ~$0.04–$0.07/M | Compute cost only, not per-request | High-volume, cost-optimized, or compliance-isolated |
The Hidden Cost: Data Transfer Egress
Per-request pricing is only part of the bill. API responses consume egress bandwidth, and cloud providers charge $0.09–$0.12 per GB for internet-bound traffic. With an average 12 KB response at 1,000 req/s, that's ~31 TB/month of egress data — adding roughly $2,800–$3,700/month in data transfer costs alone. This calculator includes egress estimates so the total cost projection reflects real-world billing, not just the per-request component.
Mitigation strategies: use CDN caching for cacheable API responses (CloudFront, Cloud CDN), compress payloads (gzip/Brotli reduces JSON by 60–80%), colocate services in the same region, and consider private interconnects (AWS PrivateLink, GCP Private Service Connect) for service-to-service traffic.
What "Rate Limit" Actually Means for Cost Modeling
An API rate limit expressed in requests per second is the sustained steady-state ceiling. Real-world traffic is bursty — diurnal patterns, event-driven spikes, and retry storms all create peaks above the sustained average. This calculator includes a burst ratio to model the peak capacity that your gateway must provision:
| Traffic Pattern | Typical Burst Ratio | Example |
|---|---|---|
| Internal tools, cron-driven | 1.0–1.2× | Steady rate, predictable |
| SaaS with diurnal users | 1.5–2.0× | Peak at 9am–5pm business hours |
| Consumer app with notifications | 3.0–5.0× | Push notification triggers simultaneous opens |
| Event-driven / flash sales | 10–50× | Ticketmaster-style on-sale stampedes |
Managed gateways handle bursts transparently (you pay per request regardless of pattern), but self-hosted gateways must be provisioned for peak capacity. A 1,000 req/s sustained rate with a 5× burst ratio needs a self-hosted tier sized for 5,000 req/s peak — which means larger instances or more replicas driving up the fixed compute cost.
WebSocket and gRPC: Different Cost Dynamics
Persistent protocols change the cost equation. WebSocket APIs are priced per message and per connection-minute, not per HTTP request. A WebSocket service with 10,000 concurrent connections exchanging 50 messages/second each generates 1.3 billion messages/month — at AWS WebSocket pricing ($1.00/M messages + $0.25/M connection-minutes), that's ~$4,900/month, fundamentally different from the REST model. gRPC over HTTP/2 benefits from multiplexing and binary payloads (Protobuf), reducing both request count (fewer round trips) and data transfer volume (smaller payloads vs JSON).
The Breakeven Volume: When Self-Hosting Wins
Managed gateways trade operational simplicity for per-request pricing. There is a clear crossover point where self-hosting becomes cheaper:
| Managed Gateway | Breakeven req/s | Monthly Volume | Self-Hosted Alternative |
|---|---|---|---|
| AWS REST API Gateway ($3.50/M) | ~15 req/s | ~39M requests | Single c5.large NGINX (~$62/mo) |
| AWS HTTP API Gateway ($1.00/M) | ~50 req/s | ~131M requests | Single c5.large NGINX (~$62/mo) |
| Azure APIM Premium ($1.20/M) | ~100 req/s | ~263M requests | HA pair c5.xlarge (~$248/mo) |
The breakeven shifts based on team size, compliance requirements, and whether you already operate Kubernetes clusters that can absorb the self-hosted gateway workload. For organizations running their own K8s, adding an Envoy/Kong sidecar has near-zero marginal compute cost — making the breakeven effectively 0 req/s.