Instant SLA Uptime Downtime Calculator: Know Your Nines

Uptime / SLA Calculator

Convert SLA percentages ↔ downtime budgets instantly. No server. No tracking.

Quick:
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📊 Standard SLA Reference Table

Common SLA tiers with allowed downtime. Uses 365.25d/year and 30.44d/month averages.

SLA Nines Per Year Per Month Per Week Per Day

Built by VahaC — 100% client-side, no data sent anywhere.

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Running self-hosted services means you care about availability — but turning a number like 99.9% into real human time isn’t always obvious. That’s exactly what this SLA uptime downtime calculator is for: enter any SLA percentage and instantly see how many hours, minutes, and seconds of downtime that allows per year, month, week, and day. Or flip the direction — enter your actual outage duration and find out which SLA tier you’re hitting.

What This SLA Uptime Downtime Calculator Does

This SLA uptime downtime calculator runs entirely in your browser. No backend, no API calls, no data collection. Here’s what it gives you:

  • 🔄 Two modes — SLA → Downtime and Downtime → SLA
  • ⚡ Quick preset buttons for the most common tiers: 90%, 99%, 99.5%, 99.9%, 99.95%, 99.99%, 99.999%, 99.9999%
  • 📊 Full downtime budget — per year, month, week, and day, formatted as Xd Xh Xm Xs
  • 🔵 Nines rating — a ●●●○○○ dot indicator showing how many nines your SLA has, from One Nine to Seven+ Nines
  • 🎨 Color-coded results — green for four nines and above, cyan for three nines, amber for two, red below that
  • 📋 Reference table — all standard SLA tiers in one place, useful for comparing contracts or planning maintenance windows
  • 🔗 Shareable URLs — the calculated SLA is stored in the URL hash so you can bookmark or share a specific result

How to Use It

  1. Choose a mode — SLA → Downtime or Downtime → SLA — using the toggle at the top
  2. Either type in your SLA percentage, or tap one of the quick preset buttons
  3. Press Calculate (or hit Enter on the keyboard)
  4. Read off your downtime budget per period in the result card
  5. Click Copy Result to grab a formatted text summary, ready to paste into a ticket, README, or runbook

For the reverse mode, enter the outage duration, pick a time unit (seconds, minutes, hours, or days), choose the reference period, and calculate.

Understanding “The Nines” ⑨

SLA tiers are commonly described by how many consecutive nines appear in the percentage. The SLA uptime downtime calculator visualises this as a dot rating and a text label:

  • One Nine — 90% — ~36.5 days/year — absolute minimum for any non-critical tool
  • Two Nines — 99% — ~3.65 days/year — typical for personal home lab services
  • Three Nines — 99.9% — ~8h 45m/year — standard for SMB-grade cloud services
  • Four Nines — 99.99% — ~52m/year — enterprise-grade, requires redundant architecture
  • Five Nines — 99.999% — ~5m 15s/year — telecom-grade, extremely costly to maintain

For most self-hosted setups running on a single machine, three nines is a realistic and respectable target. The SLA uptime downtime calculator uses a Julian year (365.25 days) and an average month (30.44 days) for all calculations — the same values used by most cloud providers in their contracts.

Practical Use Cases 🛠️

🖥️ Home lab uptime planning — Before patching your Proxmox setup, use the SLA uptime downtime calculator to understand how much downtime budget you actually have per month before exceeding three nines. Spoiler: it’s about 43 minutes.

🔒 Self-hosted password managers — Services like self-hosted Bitwarden need predictable availability. Calculate what 99.9% uptime means in practice before promising it to your household.

🐳 Container update scheduling — Planning rolling restarts across hardened Docker containers? Know your per-service downtime allowance before scheduling a maintenance window.

🌐 VPN availability — If your self-hosted WireGuard VPN goes down more often than expected, run the reverse calculation and find out which SLA you’re actually delivering vs. what you promised.

📑 SLA contract review — Comparing vendor proposals? Paste both SLA values into the SLA uptime downtime calculator and compare the downtime budgets side-by-side in the reference table.

Privacy, Ads, and Data Policy

  • ✅ 100% free — no account, no registration required
  • ✅ No data storage — your inputs never leave the browser
  • ✅ No ads — no tracking pixels, no watermarks, no affiliate links
  • ✅ Client-side only — this SLA uptime downtime calculator makes zero external API calls

Open Source and Self-Hosting

The tool is a single folder — index.html, style.css, script.js — and deploys anywhere static files are served. No build step, no dependencies, no framework. Grab it from GitHub, host it yourself, or fork it freely.

Browse all client-side utilities at vahac.com/tools/.