Why Cost-Per-Active-Hour Became Our North Star Metric — And How We Cut AI Spend 65% in 60 Days

TL;DR: Monthly subscription ($20, $100) hides real efficiency. We track cost per active coding hour (tool cost ÷ trackmy.codes active hours). May: $3.50/hr. June (post-credit-pool + workflow split): $1.22/hr. The metric exposes waste no invoice shows. Full breakdown →

The Context

Two-dev team. Jan–Apr 2026: Cursor Pro ($40/mo team) + Anthropic API ($200–300/mo) + Copilot ($40/mo) = $280–370/mo. Felt like “cost of doing business.” No visibility into actual AI-assisted coding time vs IDE-open time. April: installed trackmy.codes (local, $29/yr) across both machines. The number shocked us.

The Metric: Cost Per Active Hour (CPAH)

CPAH = (Sum of all AI tool costs for month) / (Total active coding hours from trackmy.codes)

Active hour = 30-second windows with keystrokes + AI request/response. Idle (PR reviews, meetings, reading, coffee) excluded.

Month	Tool Stack	Tool Cost	Active Hours (trackmy.codes)	CPAH
Jan	Cursor + API + Copilot	$320	68 hrs	$4.71/hr
Feb	Cursor + API + Copilot	$350	72 hrs	$4.86/hr
Mar	Cursor + API (Copilot 4x)	$420	75 hrs	$5.60/hr
Apr	Cursor + API + trackmy.codes	$340	97 hrs	$3.51/hr
May	Cursor + API + trackmy.codes	$287	82 hrs	$3.50/hr
Jun	Claude Code pool + Windsurf + Codex	$135	111 hrs	$1.22/hr

June changes: (1) Switched to Claude Code credit pool ($100 fixed), (2) Added Windsurf ($30) for daily editing, (3) Codex in existing ChatGPT Plus, (4) Dropped Copilot, (5) Cline BYOK for model-flexible tasks (~$15 variable).

The Pivot Point

April 28: trackmy.codes dashboard showed Dev A: 158 hrs IDE-open, 47 hrs active (70% idle). Dev B: 134 hrs open, 35 hrs active (74% idle). We were paying for presence, not production. Same week: Anthropic credit pool announced. Math: $100 fixed for ~47 active hrs = $2.13/active-hr including model cost. But wait — credit pool covers Sonnet; Opus extra. Adjusted for Opus flag protocol: $140 projected / 47 hrs = $2.98/hr. Still 15% better than May.

But the real unlock: Workflow split (Claude Code for autonomy, Codex for persistence, Windsurf for editing) raised active hours to 111 hrs in June (devs less frustrated, more flow). CPAH dropped to $1.22 — not just from cheaper tools, but from more active hours per dollar.

What We Use Now

Monthly CPAH Review (first Monday, 30 min):

# 1. Pull active hours
trackmycodes stats --since 30d --by-person --format csv > /tmp/active-hours.csv

# 2. Pull tool costs (manual entry in Notion, or script later)
# 3. Calculate CPAH per person + team
# 4. If team CPAH > $2.00: investigate tool mismatch
# 5. If individual CPAH > $3.00: 1:1 workflow audit

Notion Dashboard (shared):

• Team CPAH trend line (6-month rolling)
• Per-person CPAH + active hours
• Tool cost breakdown (fixed vs variable)
• Active hours by tool (Cursor vs Codex vs Claude Code vs Windsurf)
• Threshold alerts: Team CPAH > $2.00 = workflow review; Individual > $3.00 = pairing session

When You’d Choose Differently

• Teams optimizing for speed, not cost: CPAH may rise; that’s fine if velocity justifies it.
• Fixed-budget environments: CPAH is a lagging indicator; use hard caps (credit pool, flat-rate) instead.
• Non-coding AI use (docs, research, design): trackmy.codes only tracks coding; use separate metric.

Tool Crucible Rating

Dimension	Rating (1–5)	Notes
Overall	5	Single metric that aligns tooling, workflow, and budget
Ease of Use	4	trackmy.codes auto-collects; Notion dashboard 1-hr setup
Value	5	65% cost reduction + 35% more active hours in 60 days
Support	N/A	Internal metric; trackmy.codes support 4/5

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This is part of our AI Coding Tool Evaluation series. See full breakdown: Cost Per Active Hour: The Metric That Cut Our AI Spend 65%