Do a Number Trick to Guess Someone's Age

There are lots of number tricks you can do by using math. You can give someone a particular set of instructions and calculations and their current age can be deduced. To them it appears as though you are performing a magic trick, but all you need to know are the instructions. The math will work every time. Another set of instructions can be given to get the month and day of their birth. You can also use math to appear to guess the age of a stranger.

Steps

Deducing Someone’s Age Using a Selected Number

1. Ask your friend to choose a number between two and ten. To make the game more fun, you might ask them how many times per week they would like to have ice cream, go out to eat, or something similar. Once they have a number in mind, ask them to announce it.
   • Say that they choose the number 6. This will be the example used throughout this method.
2. Multiply the given number by two. You can do this math by hand or your friend can use a calculator for the rest of the trick. Explain to your friend that they must hit the equal (=) button after each instruction you give.
   • Example: 6 x 2 = 12.
3. Add five to the answer.
   • Example: 12 + 5 = 17.
4. Multiply that number by 50.
   • Example: 17 x 50 = 850.
5. Ask your friend if they’ve already celebrated their birthday for this year. If their birthday has passed already, then tell them to add 1767 to the prior result. If their birthday is coming up, then ask them to add 1766 to the prior result.
   • Example 1: (with prior birthday): 850 + 1767 = 2617.
   • Example 2: (with upcoming birthday): 850 + 1766 = 2616.
   • Be aware that the numbers are for the year 2017. If you are performing these calculations in a later year, then you would use the numbers 1768 and 1767 for 2018, 1769 and 1768 for 2019, and so on.
     
6. Subtract the year that they were born.
   • Example 1: 2617 - 1981 (year of birth) = 636
   • Example 2: 2616 – 1981 (year of birth) = 635
7. Look at your final answer. The first digit, the one in the hundred’s place, will be the original one chosen. The remaining two numbers will reveal your friend’s age.
   • Example 1: The answer is 636. 6 was the original number chosen. 36 is the current age.
   • Example 2: The answer is 635. 6 was the original number chosen. 35 is the current age.

Using a Calculator to Find Someone’s Age

1. Ask the person to multiply the first number of their age by five. For the sake of this example, let’s say the person is 35 years old. They can use a calculator or scratch paper for this. Let the person know that they must hit the equal (=) button after each instruction you give.
   • Example: 5 x 3 = 15.
2. Tell them to add three.
   • Example: 15 + 3 = 18.
3. Tell them to double the resulting figure.
   • Example: 18 x 2 = 36.
4. Have them add the second number of their age to that number.
   • Example: 36 + 5 = 41.
5. Tell them to subtract six. The answer will be their current age.
   • Example: 41 – 6 = 35.

Using a Calculator to Deduce the Month and Date of Birth

1. Enter the number seven. Then, multiply it by the month of their birth. For this example, let’s say their date of birth is May 28, 1981.
   • Example: 7 x 5 (birth month: May) = 35.
2. Subtract one. Then, multiply by 13.
   • Example: 35 – 1 = 34
   • Then: 34 x 13 = 442.
3. Add the day of their birth.
   • Example: 442 + 28 = 470.
4. Add three. Then, multiply by 11.
   • Example: 470 + 3 = 473.
   • Then: 473 x 11 = 5,203.
5. Subtract the month of their birth. Then, subtract the day of their birth.
   • Example: 5,203 - 5 (May) = 5,198.
   • Then: 5,198 – 28 = 5,170.
6. Divide by 10. Then, add 11.
   • Example: 5,170 ÷ 10 = 517.
   • Then: 517 + 11 = 528.
7. Divide by 100. The first digit, before the decimal, is their birth month (May). The digits after the decimal denote the day of birth (28).
   • Example: 528 ÷ 100 = 5.28.

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• Find out Someone's Birthday

Warnings

• Make sure to take your time with the math or you may miss a step and end up with an incorrect result.

Sources and Citations

See also

• Do a Number Magic Trick
• Do a Math Magic Trick
• Do a Simple Number Mind Trick
• Do a Cool Mathematical Mind Reading Trick
• Do a Mind Reading Magic Number Trick
• Perform a Card Trick Using Math
• Trick Friends with the 5000 Number Adding Trick