We ordered a 99 years old birthday card for a very special cousin who is 99 today. The card itself was of good quality, however, the manufacturer clearly does not employ a mathematician. The card states that she will be 36,281.5 days old on her birthday. This is clearly wrong as multiplying 99 by x.25 will always give a value ending in 0.75 rather than 0.5. Birthdays are whole days rather than fractions and so the exact number of days depends upon which year they were born, as there are 97 leap years every 400 years. This makes an average year length of 365.2425 days. Our grand-daughter will be one next month, making her 365 days old on her birthday but she would have been 366 days old on her first birthday if she was born in 2015 instead of 2017. To see exactly how many leap years my wife’s aunt has lived through, I put her details into Excel. She was born on 11th September 1919. If I subtract 11-Sep-2018 from 11-Sep-1919 in Excel, I get a figure of 36,160, which comprises of 74 regular years and 25 leap years. If I then divide the printed value of 36,281.5 by 365.25, I get 99.3333. Hopefully she will still be with us on January 11th 2019, to enjoy her 99 1/3 card!!!