What is Off By Ten?

Off By Ten is a free daily estimation game. Every day at midnight you get five new questions, each with a numeric answer — how heavy is a blue whale's heart, how many satellites orbit Earth, how long did the Roman Empire last? You don't need the exact number. You need to be close.

How to play

• Read the question and type your best guess — shortcuts like 3.5k, 12m, and 1.2b work.
• Score by closeness, not exactness. Land within 5% for a 🎯 bullseye (20 pts), within 1.5× for 🟩 (15), within 3× for 🟨 (10), within 10× for 🟧 (5). More than ten times off? That's 🟥 zero — you were off by ten.
• Five questions, 100 points max. Share your emoji scorecard and come back tomorrow to keep your streak alive.

Frequently asked questions

When does a new puzzle come out?

A new puzzle unlocks at midnight in your local timezone, every day. One puzzle per day — that's the game.

Do I need an account?

No. Your streak and stats are saved privately on your device. No sign-up, no email, nothing to install.

Are the answers accurate?

Every question is fact-checked against credible sources before it ships, and each reveal names its source. Many real-world quantities are estimates by nature, so answers use the best-sourced central value — which is exactly why the game scores by closeness instead of exactness.

Is Off By Ten free?

Completely free, playable in any browser, on any device.

Who makes this?

Off By Ten is a small independent project. Every question is verified against credible sources before it ships, and each reveal names its source — more on the about page.