posthog-cost-tuning

PostHog Cost Tuning

Overview

PostHog Cloud pricing is event-based: 1M events/month free, then usage-based pricing beyond that. Session recordings, feature flag evaluations, and surveys each have their own free tiers. The biggest cost drivers are typically $autocapture events, $pageview on high-traffic pages, and bot traffic. This skill covers specific techniques to reduce event volume without losing analytical value.

Prerequisites

• PostHog Cloud account with billing access
• Application instrumented with posthog-js
• Understanding of which events drive your analytics

PostHog Cloud Free Tiers (2025)

Product	Free Tier	Overage
Product analytics	1M events/month	~$0.00031/event
Session recordings	5K sessions/month	~$0.04/session
Feature flags	1M API requests/month	~$0.0001/request
Surveys	250 responses/month	~$0.10/response

Instructions

Step 1: Audit Current Event Volume

set -euo pipefail
# See which events consume the most quota (last 30 days)
curl "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID/query/" \
  -H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "query": {
      "kind": "HogQLQuery",
      "query": "SELECT event, count() AS total FROM events WHERE timestamp > now() - interval 30 day GROUP BY event ORDER BY total DESC LIMIT 20"
    }
  }' | jq '.results[] | {event: .[0], count: .[1]}'

Step 2: Tune Autocapture

$autocapture is often the largest event volume. Restrict it to only useful interactions.

import posthog from 'posthog-js';

posthog.init(process.env.NEXT_PUBLIC_POSTHOG_KEY!, {
  api_host: 'https://us.i.posthog.com',
  autocapture: {
    // Only capture click and submit events (skip change, scroll, etc.)
    dom_event_allowlist: ['click', 'submit'],
    // Only capture meaningful elements
    element_allowlist: ['a', 'button', 'form', 'input[type=submit]'],
    // Only capture elements with this CSS class
    css_selector_allowlist: ['.track-click', '[data-track]'],
    // Skip internal/admin pages entirely
    url_ignorelist: ['/admin', '/health', '/api/internal', '/_next'],
  },
});

Step 3: Event Sampling with before_send

posthog.init(process.env.NEXT_PUBLIC_POSTHOG_KEY!, {
  api_host: 'https://us.i.posthog.com',
  before_send: (event) => {
    // 1. Always send business-critical events (no sampling)
    const critical = ['purchase', 'signup', 'subscription_started', 'subscription_canceled', 'error'];
    if (critical.includes(event.event)) return event;

    // 2. Drop bot traffic entirely
    const ua = navigator?.userAgent?.toLowerCase() || '';
    if (/bot|crawler|spider|scrapy|headless|phantom|puppeteer/i.test(ua)) {
      return null;
    }

    // 3. Sample pageviews to 25% on high-traffic pages
    if (event.event === '$pageview') {
      const highTraffic = ['/', '/pricing', '/blog'];
      const url = event.properties?.$current_url || '';
      if (highTraffic.some(p => url.endsWith(p))) {
        return Math.random() < 0.25 ? event : null;
      }
      return event; // Keep other pageviews at 100%
    }

    // 4. Sample autocapture to 20%
    if (event.event === '$autocapture') {
      return Math.random() < 0.2 ? event : null;
    }

    // 5. Sample pageleave to 50%
    if (event.event === '$pageleave') {
      return Math.random() < 0.5 ? event : null;
    }

    return event; // Keep all other events
  },
});

Step 4: Optimize Session Recording Costs

posthog.init(process.env.NEXT_PUBLIC_POSTHOG_KEY!, {
  api_host: 'https://us.i.posthog.com',
  session_recording: {
    // Record only 10% of sessions (saves 90% on recording costs)
    sampleRate: 0.1,
    // Don't record sessions shorter than 5 seconds (bounces)
    minimumDurationMilliseconds: 5000,
    // Record 100% of sessions with errors (most valuable for debugging)
    // This is configured in PostHog dashboard under Session Replay settings
  },
});

// Alternatively: disable recording for non-paying users
posthog.init(process.env.NEXT_PUBLIC_POSTHOG_KEY!, {
  api_host: 'https://us.i.posthog.com',
  disable_session_recording: true, // Start disabled
});

// Enable only for paying users
if (user.plan !== 'free') {
  posthog.startSessionRecording();
}

Step 5: Monitor Usage and Set Alerts

set -euo pipefail
# Check current month's event usage
curl "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID/query/" \
  -H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "query": {
      "kind": "HogQLQuery",
      "query": "SELECT count() AS total_events, uniq(distinct_id) AS unique_users, count() / dateDiff('"'"'day'"'"', toStartOfMonth(now()), now()) AS events_per_day FROM events WHERE timestamp > toStartOfMonth(now())"
    }
  }' | jq '.results[0] | {
    total_events: .[0],
    unique_users: .[1],
    avg_events_per_day: .[2],
    projected_monthly: (.[2] * 30),
    over_free_tier: (.[2] * 30 > 1000000)
  }'

// Automated cost monitoring
async function checkPostHogBudget() {
  const result = await queryPostHog(`
    SELECT count() AS events_this_month
    FROM events
    WHERE timestamp > toStartOfMonth(now())
  `);

  const eventsThisMonth = result.results[0][0];
  const FREE_TIER = 1_000_000;
  const projectedMonthly = eventsThisMonth / (new Date().getDate() / 30);

  if (projectedMonthly > FREE_TIER * 0.8) {
    // Alert: approaching free tier limit
    await sendSlackAlert(`PostHog usage alert: ${Math.round(projectedMonthly / 1000)}K events projected this month (free tier: 1M)`);
  }
}

Cost Reduction Estimates

Technique	Typical Reduction	Impact on Analytics
Restrict autocapture elements	40-60%	Low (keep meaningful clicks)
Filter bot traffic	10-30%	None (bots are noise)
Sample $pageview on high-traffic	20-40%	Low (trends still accurate)
Session recording at 10%	90% on recordings	Medium (fewer sessions to review)
Disable $pageleave	15-20%	Low (rarely analyzed)

Error Handling

Issue	Cause	Solution
Event volume spike	New feature without volume estimate	Forecast events before launch
Bill higher than expected	Bot traffic	Add bot filtering in before_send
Missing critical events	Sampling too aggressive	Exclude revenue events from sampling
Free tier exceeded mid-month	Autocapture too broad	Restrict to .track-click elements only

Output

• Autocapture restricted to meaningful interactions
• Event sampling reducing volume by 30-50%
• Bot traffic filtered
• Session recording sampled to 10%
• Budget monitoring with alerting

Resources

• PostHog Pricing
• PostHog Autocapture Config
• PostHog before_send
• Session Recording Control