What “combined age” really means
Add up the ages of two people and you get a number that grows twice as fast as either of you. Couples often notice it when they reach a round figure together, such as 100, and some families mark the day with a party. Grandparents can reach a combined 150 or 160 with ease, and a big family can pass 200 sooner than anyone expects. The bar above shows each person as a coloured block, so you can see who is carrying most of the total and how close you are to the next round number.
Because the combined figure grows by one year per person per year, the milestones come round quickly. A couple reaches each new 50 years together every 25 years; a family of five reaches it every 10.
How we calculate it
For each person we count the days from their birth date to today. We add those up and divide by 365.2425, the average length of a calendar year, which gives a combined age that is correct to the day. To find a milestone date, we look for the first day on which the total reaches that number of years. If someone in the group had not yet been born, they add nothing until their birthday, which matters for milestones in the past.
| People | Combined age grows by | Time between 50-year milestones |
|---|---|---|
| 2 | 2 years every year | 25 years |
| 3 | 3 years every year | about 16 years 8 months |
| 4 | 4 years every year | 12 years 6 months |
| 5 | 5 years every year | 10 years |
Worked example. A couple born on 12 April 1990 and 18 June 1992 had a combined age of 70 years and 11 months on 30 October 2026. They reach 100 together on 16 May 2041, when one of them is 51 and the other 48.
Ways to mark it
A combined 100 is a lovely excuse for a joint birthday, especially for a couple whose birthdays fall far apart. Some families gather for a combined 200 or 300 with grandparents, parents and children together. The date is precise, so you can put it in the calendar years ahead.
Questions people ask
How do you add up ages exactly?
We add together the number of days each person has been alive and divide by the average length of a year, 365.2425 days. That gives a combined age to the day, rather than adding whole years, which can be out by almost a year for each person.
Why does our combined age grow so fast?
Every person adds one day of age every day. Two people add two days, so a couple’s combined age goes up by two years every year. A family of five ages five years in every calendar year.
Can I include people who have died, or pets?
You can include anyone you like, though for someone who has died the total keeps counting as if they were still here. For pets it works well as a bit of fun.
Is anything saved?
Your own birthday is remembered on this device so other pages can use it. The other names and dates stay only while the page is open.
Sources. Gregorian calendar; average year of 365.2425 days. Calculations run in your browser; nothing you enter is sent anywhere.