Anniversaries grant your nation a population happiness bonus that increases as your nation gets older. Nations created before noon server time will have their anniversaries on the days listed; nations created after noon will have them on the day after. Below are the anniversary dates:

• One week (7 days)
• Two weeks (14 days)
• One month (30 days)
• Two months (60 days)
• Three months (90 days) - +2 happiness
• Six months (180 days) - +4 happiness
• One year (365 days)

Anniversaries are the best days to collect taxes because the happiness bonus is applied to every day of taxes that you have saved.