How to do the 1089 number trick

Seal the number 1089 in an envelope. Ask a helper to think of any three-digit number whose first and last digits differ by 2 or more, reverse it, subtract the smaller from the larger, then reverse the answer and add the two together. However they start, they finish on 1089, and your prediction is already waiting. It’s arithmetic, not sleight of hand, so it works over the phone, on a video call or across a dinner table.

The 1089 trick is a number trick that feels like mind reading. It needs nothing but a pen, paper and, if you like, a calculator for your helper. This guide covers the steps, the one rule you must give your helper, the maths behind it and a few ways to dress it up.

What does the audience see?

You hand someone a sealed envelope and ask them not to open it. They secretly choose a number and do a little arithmetic, out of your sight. When they announce their final answer, they open the envelope. Inside is the same number: 1089.

What do you need?

• A slip of paper with 1089 written on it, sealed in an envelope (or written on the back of a business card, face down on the table).
• Paper and a pen for your helper, or the calculator on their phone.

How do you do it, step by step?

1. Set the prediction. Put the envelope in view, or hand it to someone to hold.
2. Choose a number. Ask your helper to write any three-digit number where the first and last digits differ by 2 or more. For example, 732.
3. Reverse it. Write the same digits backwards: 237.
4. Subtract. Take the smaller number from the larger: 732 − 237 = 495.
5. Reverse the answer. 495 becomes 594.
6. Add. 495 + 594 = 1089.
7. Reveal. Ask for their final number, then have them open the envelope.

Try it yourself with a few numbers before you show anyone. 782 gives 782 − 287 = 495, and 495 + 594 = 1089 again.

What is the one rule you must give?

The first and last digits must differ by at least 2. If they are the same (like 414), the reversed number is identical and the subtraction gives zero. If they differ by exactly 1 (like 201), the subtraction gives 99, and the trick only works if your helper writes it as 099, so that its reverse is 990 and 099 + 990 = 1089. Asking for digits that differ by 2 or more avoids both problems.

A friendly way to say it: “Pick any three-digit number, but make sure the first and last digits are not the same and not next to each other, like 3 and 4.” Then check their number quietly if you can, or simply ask them to start again if the subtraction gives 99 or 0.

Why does it always come to 1089?

Write the starting number as three digits, with the first digit bigger than the last. When you subtract the reversed number, something always happens: the middle digit of the answer is always 9, and the first and last digits of the answer always add up to 9. You can see it in the examples: 495 (4 + 5 = 9), 297 (2 + 7 = 9), 693 (6 + 3 = 9).

So the answer always looks like a9b, where a + b = 9. Reverse it and add, and the hundreds give 9, the tens give 18, and the units give 9. Put together, 900 + 180 + 9 = 1089, every time.

You don’t need to explain any of this to your audience. Knowing it just gives you confidence that the trick can’t fail if the rule is followed.

How do you make it feel like mind reading?

• Give them freedom. Let them choose any number they like, and turn your back while they do the sums. The more freedom they feel, the stronger the ending.
• Hide the number in something else. Instead of writing 1089, you can prepare something linked to it in advance: a page number, a date, or the 1,089th word of a story. Magicians often use the number this way, so the prediction doesn’t look like arithmetic.
• Do it only once per person. If the same person does it twice and gets 1089 again, the secret is out.
• Perform it remotely. Because you never need to see their number, it works well on a phone or video call. Our guide to magic on a video call covers the rest.

Where does the trick come from?

We haven’t found a reliable earliest source for the 1089 trick, so we won’t guess. What we can say is that it is widely used in magic, including in book tests. David Acheson, writing in Plus magazine, says he first met it in 1956, at the age of ten, in an article titled “Abracadabra! Uncle Jack turns you into a Conjuror!”

What helps you take it further?

• Mathematical Recreations and Essays by W. W. Rouse Ball is a free 394-page PDF (tenth edition, 1922) of mathematical puzzles and amusements, including arithmetical card tricks and magic squares. Its description calls it a favourite source for magicians who build self-working and number-based effects.
• Puzzles Old and New by Professor Hoffmann is a free 416-page PDF (1893) with arithmetical teasers among its puzzles, with the solutions.

Ready for more mind reading? Read our beginner’s guide to mentalism, or try another self-working classic, the 21-card trick.

Frequently asked questions