Dev & engineering · free calculator
p99 latency vs cost tradeoff
Quantify monthly cost of cutting p99 latency from baseline target — compute scaling, caching, edge deployment, and faster instance tiers.
Additional monthly cost
Show the work
- Annual additional cost$281,718
- p99 improvement %70.6%
- Cost per 100ms improvement$3,913
Latency improvement isn't free
Cutting p99 latency from 850ms to 250ms is achievable but typically requires 2-3x more compute, plus caching, plus edge deployment. The math reveals whether the latency improvement is worth the spend.
The cost stack
To cut latency in half, the typical mix:
- Vertical scaling (faster CPU): adds 30-50% to compute cost
- Horizontal scaling (more replicas): adds 50-100% to compute cost (parallelism + load distribution)
- Caching layer (Redis / Memcached): $500-2000/mo flat for many use cases
- Edge deployment (CloudFront / Fastly / Cloudflare Workers): $500-5000/mo flat for typical SaaS
Default scenario
Cutting 850ms → 250ms (70% reduction) with 250% scaling factor + caching + edge:
- Compute scaling: $12k × 250% × 70% = $21k extra
- Caching: $800
- Edge: $1,500
- Total: $23,300/mo extra ($280k/yr)
That's $33 per 100ms reduction per month — only worth it if user-facing latency drives meaningful conversion or revenue.
When latency improvement pays back
- E-commerce: 100ms latency = 1% conversion drop (Amazon study). For a $10M GMV site, 100ms = $100k/yr revenue lift.
- B2B SaaS productivity tools: latency >300ms creates 'feels broken' perception. Worth fixing for retention.
- Real-time apps (chat, gaming): latency IS the product. Spend whatever it takes.
When latency improvement doesn't pay
- Background batch jobs: nobody waits, latency irrelevant
- Low-traffic admin tools: 5x cost for 5x speed used by 10 employees not worth it
- Already at 100ms: getting to 50ms costs 10x for marginal user-perceived improvement
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