Decimal birthdays can be celebrated using any time unit (years, months, days, hours, minutes, seconds), however the most common form of celebration uses days. The main form of celebration falls on the occurrence of every 1000th day of a person's life. The standard practise is to count the day of birth as day zero and then count upwards from that day onwards.

This form of celebration has become more popular since the widespread use of computers and the internet which have made the calculation of the decimal birthday easier to make.

However, the celebration of a decimal birthday has some traditional significance in some cultures, for example in Korea it is common to celebrate the Bek-Il or the 100th day of life. This tradition was born from a time of high infant mortality when many babies would die before three months of age. As a result the 100th day is a celebration of life as the baby has survived the difficult first 100 days of life.

A Tkday is your 10,000th day on earth. It's when your day count irreversibly ticks over to five figures and you find yourself at a point in your life from which there is no going back.

On your Tkday you are an adult. Yes, some people become grown ups when they are 21, 18 or even 16 years old but really, you're not a proper one till you're just over 27 and a third. It's then that you should really know how to change a tyre/fuse/partner, not feel too awkward when you meet other adults and have vague but nagging thoughts about starting a pension. It's a time for celebration.

School starts at about 2,000 days. Puberty is experienced between your 5,000th and 7,000th days. Life begins after 15,000 days. Retirement comes at around 24,000 days On average people will live to about 30,000 days.