Question 1

What is a latency budget and why is it important?

Accepted Answer

A latency budget is the maximum acceptable response time for a system operation. It's important because it ensures consistent user experience, sets performance goals for development teams, helps identify bottlenecks before they impact users, and enables data-driven performance decisions. Without latency budgets, systems often degrade slowly until users notice and leave.

Question 2

What does P95 mean and why use it instead of average?

Accepted Answer

P95 (95th percentile) means 95% of requests complete within that time. We use P95 instead of average because it captures the long tail of slow requests that users actually experience. An average of 200ms might sound good, but if 5% of users wait 2 seconds, those users will have a poor experience. P95 ensures we optimize for the majority while still paying attention to edge cases.

Question 3

How do I set realistic latency budgets?

Accepted Answer

Start with user expectations: 100ms for instant feel, 100-300ms for fast, 300-500ms for acceptable. Then subtract: Frontend (200ms), Backend (200ms), Network (200ms), Database (100ms) = 700ms total. Monitor actual performance and adjust based on real data. Consider your specific use case - checkout pages might need stricter budgets than search results.

Question 4

What components should I track in the ledger?

Accepted Answer

Track all components that contribute to the user's perceived response time: DNS lookup, TCP connection, TLS handshake, server processing, database queries, API response, content download, JS parse/execute, render/paint. These are the building blocks that make up your P95 target - if any component is over budget, it contributes to the overall latency.

Question 5

How does the traffic impact estimate work?

Accepted Answer

The traffic impact figures are illustrative, not measured. The calculator scales an estimated 'slow users' percentage and bounce rate by how far your total current latency overshoots the P95 target. They are meant to communicate relative severity, not predict exact business outcomes. Use real RUM (Real User Monitoring) data for production decisions.

Question 6

What action items does the calculator generate?

Accepted Answer

Action items highlight components that exceed their budget. Each item shows what's over budget, by how much (percentage and absolute), and which layer needs optimization. For example: 'Content Download is 50% over budget (+100ms)'. These are your optimization priorities - focus on the largest overshoots for maximum impact.

Component	Current	Budget	Δ	Status
DNS Lookup	20ms	30ms	-10ms	OK
TCP Connection	50ms	60ms	-10ms	OK
TLS Handshake	80ms	100ms	-20ms	OK
Server Processing	200ms	150ms	+50ms	OVER
Database Query	150ms	100ms	+50ms	OVER
API Response	50ms	50ms	0ms	OK
Content Download	300ms	200ms	+100ms	OVER
JS Parse & Execute	400ms	300ms	+100ms	OVER
Render & Paint	200ms	150ms	+50ms	OVER

System Latency Budget Calculator

Latency Budget Configuration

Component Budgets

Latency Budget Status

Layer Breakdown

Component Ledger

Action Items

Traffic Impact

Frequently Asked Questions

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