Quick answer
The pen starts at eight animals, according to the reported pen rules, and pen upgrades unlock more slots. Animals in your base earn Cash while you are logged out and pay out the pending income the next time you log in, which is why pen upgrades are recommended early even for casual play.
Starting capacity and upgrades
Your pen holds eight animals at the start. Additional slots are unlocked through pen upgrades bought with Cash. Because every slot is an income stream that keeps producing while you sleep, the reported advice is to buy pen upgrades early rather than saving everything for pickaxe or treadmill levels.
How offline income pays out
Animals parked in your base keep generating Cash while you are logged out. The pending income is paid out the next time you log in, so the practical routine is: fill the pen before you quit, and collect on your next session. Idle time between sessions converts into income at no extra effort.
Choosing between upgrade targets
Treadmill levels raise Speed toward the next zone gate, pickaxe levels cut the time each egg takes to break, and pen upgrades raise how many animals you can bank. The calculator page converts your treadmill progress into gate numbers, and the upgrades guide compares the three targets in detail.
What is not verified
The exact Cash-per-second values per animal and the price curve of pen upgrades are not published by any source this site trusts. The eight-slot starting capacity and the offline payout rule come from the same third-party beginner guide, so both carry the site-wide Cross-source label.
Frequently Asked Questions
How many animals can I keep?
Eight at the start, according to the reported pen rules, with more slots unlocked through pen upgrades. Animals in your base keep earning Cash while you are offline, so extra slots convert idle time into income.
Do animals earn money while I am offline?
Yes. Animals in your base generate Cash while you are logged out and pay out the pending income the next time you log in. That is the main reason pen upgrades are recommended early.
Related resources
Pets
How Break and Steal an Egg animals work: obtaining them from eggs, weight-driven income, pen capacity, merging and index rewards.
Beginner Guide
The verified first session route: treadmill, pickaxe, safest zone and your first delivered animal.
Speed Calculator
Plan which zone your Speed unlocks, how many treadmill steps the next gate needs, and how deep a merge chain goes.