# Lunar Calendar

Cakeday supports the Chinese lunar calendar (also known as the agricultural calendar or Yin calendar), making it easy to track birthdays for people who celebrate on their lunar date.

## Switching Calendar Type

When adding or editing a birthday, you will see a segmented picker at the top of the date section with two options: **Solar** and **Lunar**. Tap "Lunar" to switch. The picker provides haptic feedback to confirm your selection, and the date fields below update to the lunar format.

## Picking Month and Day

In lunar mode, the month picker shows lunar months 1 through 12 (displayed in Chinese as 正月, 二月, etc.). The day picker shows valid lunar days 1 through 29 or 30 depending on the selected month and year. Selecting a different month may adjust the available day range automatically.

## Leap Month

The Chinese lunar calendar occasionally has a leap month (闰月). Cakeday shows leap-month entries directly in the month picker when they are valid choices.

When a specific year is selected, the picker only shows the leap month that actually exists in that year. If you change the year and the selected leap month no longer exists, Cakeday automatically switches back to the regular lunar month.

When the birth year is left empty, Cakeday cannot know the exact leap-month pattern for the person's birth year. In that case, the picker offers leap months that have occurred in supported historical data and shows a hint with possible matching years, so you can verify the date later if the year becomes known.

## Year-less Birthdays

If you do not know the birth year, you can leave it empty. For solar birthdays without a year, Cakeday uses the reference year 2000 internally for date calculations. For lunar birthdays without a year, the current year is used instead, since lunar month lengths vary by year. In both cases, only the month and day are tracked for countdowns.

## Automatic Solar/Lunar Conversion

Cakeday converts between solar and lunar dates internally. When you add a lunar birthday, the app calculates the corresponding solar date for countdowns, notifications, and calendar display. The detail view shows both the solar and lunar dates side by side. Since the lunar calendar shifts relative to the solar calendar each year, the solar date of a lunar birthday will be different every year.

## Lunar Date Display Format

Lunar dates are displayed using traditional Chinese format, such as 正月十五 (first month, fifteenth day) or 八月初三 (eighth month, third day). This applies to the birthday detail view and list view.

## Sexagenary Year Cycle

When the birth year is recorded, the detail view also displays the traditional Chinese sexagenary cycle (干支) for that year, such as 甲子年 or 丙寅年. This 60-year cycle combines the 10 Heavenly Stems and 12 Earthly Branches and is a traditional way to denote years in the Chinese calendar.