Calendar and Birthday System

Overview

inZOI tracks time through a day-night cycle, a four-season rotation, and a life stage aging system. Each in-game day progresses from morning to night, seasons change every 7 days, and Zois age through 9 life stages over the course of 100 in-game days. The March 2026 update (v0.7.0) introduced a dedicated 28-day month calendar system that tracks holidays, birthdays, and pregnancy due dates. Players can throw birthday parties as social events to celebrate aging milestones, and the calendar provides a centralized view of all upcoming events.

Because each season lasts exactly 7 in-game days, one 28-day month covers a full annual cycle of Spring, Summer, Fall, and Winter. This design gives long-running save files a clear sense of rhythm. Every month, the same holidays return, birthdays arrive on schedule, and the world transitions through all four seasons in a predictable loop.

28-Day Calendar System (v0.7.0)

The v0.7.0 update (March 26, 2026) added a full in-game calendar organized into 28-day months. This update coincided with inZOI's one-year anniversary in Early Access. The calendar serves as a centralized hub for tracking the passage of time and all important dates in a Zoi's life. It can be accessed from the Smartphone or through the main HUD.

What the Calendar Displays

The calendar UI shows multiple layers of information at a glance:

How Months Map to Seasons

The 28-day month is divided into four equal weeks of 7 days each. Each week corresponds to one season:

A pop-up notification announces the start of each new season. Because the calendar loops every 28 days, long-term saves experience a continuous cycle of seasonal change. Players who leave aging enabled will see their Zois pass through roughly three and a half full annual cycles over a 100-day lifespan.

Recurring Holidays

Players can set different holidays to recur on specific dates within the calendar. Once configured, these holidays disappear and reappear automatically as the save file progresses through time. This means that seasonal celebrations are not one-time occurrences; they come back each year cycle, giving long-term saves a sense of rhythm and tradition. Festival-themed items in Build Mode, including decorations and seasonal furniture, are tied to these recurring holidays and become available during the appropriate time window each cycle.

Seasonal Holidays

Four seasonal holidays were added alongside the calendar system. Each season has a dedicated celebration that triggers festivals across the game's cities. See the Festivals and Seasonal Events article for full details on each celebration.

When a seasonal holiday arrives, festival booths and special NPCs appear in designated areas across all three cities. Players can purchase festival-exclusive items, participate in seasonal activities, and earn unique rewards. Holiday costumes, accessories, and decorative items rotate in and out of availability based on the current season, encouraging players to revisit festivals each cycle.

Day Length Settings

The length of one in-game day can be adjusted in Settings > Simulation > Length of Day. This setting controls how quickly real time translates into in-game time, which affects how fast aging, seasons, and daily routines progress. The default is 96 minutes, which is notably longer than most life simulation games and gives players time to explore the large in-game cities.

Changing day length affects how quickly time passes during gameplay but does not change the total number of in-game days in a life stage. A Zoi who lives for 100 in-game days will always live 100 days regardless of the day length setting. Shorter day lengths are ideal for players who want to experience life stage transitions quickly, while longer settings suit players who prefer to take their time with daily routines and exploration.

Playback Speed Controls

The time panel at the bottom-left of the screen provides additional speed controls on top of the day length setting:

These speed multipliers stack with the day length setting. For example, running 4x speed on the 96-minute day length means one in-game day passes in roughly 24 real minutes. Players who want to watch Zois live out their full 100-day lifespan quickly can combine a short day length with high playback speed.

Seasons

inZOI features four seasons: Spring, Summer, Fall, and Winter. Each season lasts 7 in-game days. With the 28-day calendar, one full month equals exactly one complete cycle of all four seasons. A pop-up notification announces the start of each new season, and the calendar marks the transition days clearly.

Seasonal behavior differs by city. Dowon experiences all four seasons with noticeable temperature shifts: warmer summers and colder winters with snowfall. Bliss Bay maintains a warm climate year-round, reflecting its Southern California inspiration, so winter feels mild rather than harsh. Cahaya has a tropical climate without cold winters, keeping temperatures consistently warm across all seasons.

Temperature changes affect Zoi behavior and health. Zois automatically adjust their clothing based on the current temperature when autonomy is enabled. Wearing clothing not suited to the weather can cause illness, requiring a First Aid Kit to recover. Players can manually change the weather through the Edit City menu, though manual changes revert to the default seasonal weather after one in-game hour.

Seasons also affect available seasonal activities. Certain crops grow only in specific seasons for gardening, and the types of fish available change with the season for fishing. Snow in winter opens up winter-specific interactions in cities that experience cold weather, while summer unlocks beach activities in Bliss Bay.

Life Stage Durations

Zois age automatically as in-game days pass. Each life stage lasts a set number of days:

A Zoi's total natural lifespan spans 100 in-game days from Newborn to the end of the Senior stage. Seniors may pass away from natural causes before reaching the full 35 days, so the actual lifespan varies. At the default 96-minute day length, a full 100-day lifespan takes roughly 160 real hours of gameplay.

Players can disable aging entirely in Game Options > Simulation (added in v0.1.4). With aging disabled, Zois remain in their current life stage indefinitely and do not age up on their birthdays. This is useful for players who want to keep a household at a specific stage without time pressure. Babies born while aging is disabled will stay as Newborns until the setting is re-enabled.

Birthday System

The v0.7.0 update overhauled how birthdays work in inZOI. Every Zoi now has a birthday marked on the 28-day calendar, and the aging process is directly tied to birthday celebrations. When a birthday arrives, the Zoi transitions to their next life stage, making birthdays meaningful gameplay milestones rather than just cosmetic markers.

How Aging Works With Birthdays

When a Zoi's birthday arrives, they advance to their next life stage through one of two paths:

1. Blowing out candles during a birthday party: If the player organizes a birthday party social event, the Zoi blows out candles on a birthday cake to officially age up. This is the celebratory path that allows friends and family to participate. The moment the Zoi blows out the candles, the visual transition to the next life stage happens immediately.

2. Spending a birthday alone: If no birthday party is planned, the Zoi still ages up when their birthday arrives. They simply transition to the next life stage without a social event. The birthday is still marked on the calendar for tracking purposes, and the Memory System records the milestone regardless of whether a party was held.

Birthday Parties

Birthday parties are a type of social event that players can organize to celebrate a Zoi's aging milestone. Planning a birthday party follows the same steps as any other social event but centers around the age-up ceremony. To throw a birthday party:

1. Open the Smartphone (P key) and tap the Events app.

2. Find an open time slot on the Zoi's schedule (minimum 2-hour block required).

3. Select Make Event and choose Party as the event type.

4. Name the party, set its duration, and choose a location. Hosting at your own home gives you the most control over the setup.

5. Invite up to 10 guests, set the dress code, and choose recommended or prohibited activities.

6. Decorate the venue before guests arrive for a smoother party experience. Placing a birthday cake, balloons, and a pinata ahead of time ensures the activities are ready to go once the event starts.

Guests arrive automatically once the event begins. The host Zoi receives a notification when each guest shows up. Late arrivals are common, so starting with greeting activities gives everyone time to filter in. If the host is not present when the event timer runs out, the event may cancel automatically.

Birthday Party Activities

During a birthday party, an activity list appears with optional tasks. Completing these activities enhances the overall party experience:

• Greeting guests as they arrive at the venue.

• Blowing out candles: The birthday Zoi blows out candles on their cake, which triggers the age-up to the next life stage. This is the highlight of the party and the only activity tied to gameplay progression.

• Smashing a pinata: An interactive pinata can be set up at the party. Breaking it releases candy for party guests to collect. Note that the interaction prompt may display as 'turn on the heater' due to a known translation issue.

• Gift-giving from invited guests. Gifts are received automatically during the party.

• Taking a group photo with party attendees to commemorate the celebration. These photos are saved and can be viewed later.

None of these activities are mandatory. The Zoi will still age up even if the only completed activity is blowing out candles. However, completing more activities contributes to a better overall event rating and creates stronger positive memories for attendees.

Party Customization

When setting up any party, you can configure which activities guests are encouraged or prohibited from doing. This customization applies to birthday parties as well as other social events:

Setting a dress code helps create a consistent atmosphere. For birthday parties, recommending festive or casual attire and prohibiting fighting or rudeness keeps the mood positive. Encouraging music, dancing, and food activities tends to produce the best results for celebration-themed events.

Pregnancy Tracking

When a Zoi becomes pregnant, the calendar automatically marks the expected due date. Pregnancy lasts approximately three in-game days, with each day representing a different trimester stage as the Zoi's baby bump visibly grows. The calendar display helps players plan around the arrival of a new family member, ensuring they can prepare the home, adjust schedules, and stock up on supplies before the baby is born.

Newborns arrive at the end of the pregnancy period and immediately begin their 1-day Newborn life stage. The baby can be customized in the Create a Zoi appearance editor after birth. In the v0.7.0 update, baby Zois received several improvements: their needs were rebalanced, newborns are now born without teeth and gain them as they develop into Toddlers, and a new quick-clean interaction lets adult Zois tidy up after babies more efficiently.

Tips and Tricks

• Check the calendar at the start of each play session to see what birthdays and holidays are coming up. Planning a birthday party one day in advance gives you time to decorate and invite guests.

• If you want to age up a Zoi quickly without a party, you can reduce the day length to 48 minutes and increase playback speed. The birthday will arrive faster, and the Zoi ages up automatically even without a celebration.

• For players who enjoy the social aspect, always keep birthday cakes and pinatas in your household inventory. Having these items ready means you can set up a party venue in minutes without needing to purchase them last-minute.

• Use the pregnancy due date on the calendar to time household preparations. Building a nursery, buying baby furniture, and adjusting work schedules all benefit from advance planning.

• Disabling aging in Game Options > Simulation is useful if you want to spend extra time developing skills, careers, or relationships before a Zoi moves to the next life stage. Re-enable it when you are ready to continue the aging cycle.

• In Dowon, dress your Zois in weather-appropriate clothing before each season change to avoid illness. The calendar's seasonal markers help you anticipate when the switch will happen.

Related Features