Questions and answers
How the mirror date works, where the famous people come from, and what happens to your birth date.
What is a mirror date?
We count how many days you have been alive and go the same number of days back before your birth. Your birth sits exactly halfway between your mirror date and today — like in a mirror.
Example: someone born on January 1, 2000 had been alive for 9,803 days on November 3, 2026. 9,803 days before January 1, 2000 is February 28, 1973 — their mirror date.
Who is my time twin?
Whoever was born on your mirror date was exactly as old on the day you were born as you are today. We show three kinds of twins:
Your exact twin was born on the mirror date itself. Your near twin is the best-known person born within three days of it. Your age twin is the best-known person who, on the day you were born, was as many whole years old as you are today.
Why does my twin change every day?
Every day you are a day older, so your mirror date moves one day further into the past. Tomorrow's exact twin may be someone else. Use the arrows on the card to see who is coming up.
Where do the famous people come from, and who counts as famous?
From Wikidata, the open database behind Wikipedia. Fame is measured by how many languages Wikipedia covers a person in. People whose articles were spammed into dozens of small Wikipedias count less, according to how many library and other catalogues actually list them.
We leave out people convicted of serious crimes, serial killers, Holocaust perpetrators and victims who died as children. Borderline cases were reviewed by hand.
Someone shouldn't be there, or someone is missing?
Wikidata isn't perfect — sometimes a birth date is wrong or a description is missing. If you find a mistake or someone who shouldn't be there, write to … with the name and date. We fix it by hand.
What are day milestones?
Besides birthdays you have round numbers in days: 10,000 days, 15,000 days, and fancy ones like 11,111 or 12,345. We show your next one; you can add it to your calendar or send friends an invitation to celebrate.
Do you send my birth date anywhere?
No. Everything is calculated in your browser and only your device remembers the date; “Forget my date” deletes it. The only thing that reaches our server is the year of your mirror date (and the neighbouring years), when the data about people and events is loaded. Details are on the privacy page.
What do I give away by sharing my twin?
Sharing is always up to you, and you see what goes out first. With a little effort, your birth date can be worked out from your exact twin's name and the day you share it, and above all from a milestone's date. An age twin gives away your birth year at most. The share panel always tells you.
Where are the photos from?
From Wikimedia Commons, under free licences. Each photo shows its author and licence and links to the file's page with the full details.
Can I install BirthMirror as an app?
Yes. On a phone choose “Add to Home screen” in the browser menu (Android) or “Share → Add to Home Screen” (iPhone); on a computer use the install icon in the address bar. The app remembers your date, so you see your result as soon as you open it.
Is this about birthing mirrors?
Not that kind of birth mirror. Ours shows you who was your age on the day you were born.