Introducing a New Cat to Your Resident Cat

A second cat takes about 3 weeks to accept, not 3 days. The plan below runs 21 days in 4 stages: 3 days of scent only, 4 days of room swapping, 7 days of eating on opposite sides of a barrier, then 7 days of supervised meetings that start at 5 minutes and stop at 5 minutes. On day 1 every resource doubles: 2 litter boxes, 2 feeding stations, 2 water bowls, 2 scratching posts. Most failed introductions skip that last part, not the scent part.

Base camp: 1 room, 9 to 12 square meters

Before the carrier opens, give the new cat 1 room with the door shut: 1 litter box, 1 food bowl, 1 water bowl 1.5 meters from the food, 1 hiding box, 1 perch above 1 meter. The resident cat keeps the other 80 to 90 percent of the house, and that share is what makes the plan work. Territory loss, not the smell of a stranger, is what the resident cat is reacting to.

Put a clean towel in each bed for 48 hours, then swap them. Do not carry the new cat through the living room on day 1, and do not hold 2 cats nose to nose; a cornered 4.5 kg cat can land a bite in under 1 second, and 1 bite resets the whole timeline by 2 weeks.

Days 1 to 3: smell through the door, no eye contact

Feed both cats 30 centimeters from their own side of the closed door, 3 times a day, 10 minutes per meal. If either cat walks away from a full bowl, move it back 50 centimeters and add 2 days to this stage. Hissing at a closed door in the first 72 hours is normal; 3 days of 4 or 5 hisses per session that fade to 1 is on schedule.

Wipe the new cat's cheek with a clean sock for 20 seconds, then leave the sock beside the resident cat's bowl. Repeat in the other direction the same evening. That is the 3-day scent exchange, and it is the step owners finish in 1 hour instead of 3 days.

Days 4 to 7: swap the cats, not just the towels

Twice a day, for 20 minutes, put the resident cat in the new cat's room and let the new cat walk the rest of the house with that door shut. Two 20-minute swaps a day for 4 days covers a 2-bedroom flat. Site swapping spreads each cat's smell into the other's core area, and it buys more tolerance than 10 sessions of petting through a gap.

Week 2: a 3 cm gap between 2 bowls

Prop the door 3 centimeters open with a wedge, or fit a 90-centimeter baby gate. Feed 1.5 meters apart on day 8, then move each bowl 10 centimeters closer every 2 days until the bowls sit 30 centimeters apart on either side of the barrier. Eating 30 centimeters apart with no growl, no flattened ears, and no walk-away is the green light for week 3. If a cat takes 2 bites and leaves, you moved too fast: back up 30 centimeters and hold for 3 days.

Week 3: the first meeting lasts 5 minutes

Open the door for 5 minutes, 2 to 3 times a day. End every session at 5 minutes even when it looks friendly, because the first real fight usually starts around minute 8, after the novelty drops. Add 5 minutes per session every 3 days; by day 21 sessions run 20 to 30 minutes. Keep your hands out of it: 1 swat with claws in, then 2 cats walking away, is a pass. Chasing, cornering, or 1 cat standing over the other for 10 seconds is a fail, and you separate with a blanket, not a hand.

Two of everything, and 1 extra litter box

Resource	Minimum for 2 cats	Spacing rule
Litter boxes	3 boxes	2 rooms, never side by side
Feeding stations	2 stations	2 meters apart, facing away
Water bowls	3 bowls	1.5 meters from every food bowl
Scratching posts	2 posts, 90 cm tall	1 per shared room
High perches	3 per cat, above 1 meter	2 exit routes each

The 3-box rule is the standard n+1 formula: 2 cats, 3 boxes. Two boxes 20 centimeters apart in the same corner count as 1 box to a cat that guards them.

Setbacks: 1 stage back is normal

Hissing 3 times a day on day 10 is on track. Go back 1 stage if a cat hides more than 8 hours a day, skips 2 meals, or urinates outside the box 2 days running. Go back 2 stages if either cat blocks the litter box or guards the food bowl. Call a vet the same day if the new cat has not eaten in 48 hours, hides for 72 hours straight, or breathes with an open mouth: stress can tip a cat into hepatic lipidosis in 2 to 4 days, and that is a hospital case, not a behavior case.

Honest timelines and honest odds

Most pairs tolerate each other in 21 to 28 days and share a sofa by 3 months. About 1 in 10 pairs never become friends and settle into a cold peace with separate rooms and separate hours; that outcome is livable and does not mean the adoption failed. A resident cat over 12 years usually needs 4 to 6 weeks instead of 3, because hearing loss and joint pain make a fast newcomer harder to read; the slower version is in the senior cat adoption guide. A blind or three-legged newcomer needs the same 3 weeks plus 1 extra week of barrier time, covered in the special-needs adoption guide.

One behavior consult runs $150 to $400, and 1 extra litter box, 1 gate, and 1 feeding station add $100 to $200 to startup costs. The full first-year range sits on the cost breakdown page.

The first 7 days, in 5 steps

1. Day 1: fill 1 room with 3 resources and shut the door for 24 hours.
2. Days 1 to 3: swap bedding every 12 hours; feed 30 centimeters from the door 3 times a day.
3. Day 4: start 2 site swaps of 20 minutes each, with the new cat's door shut.
4. Day 5: log every hiss, swat, and meal; 2 skipped meals in a row means back up.
5. Day 7: if both cats eat 1 meter apart with no growl, set up week 2 at 3 centimeters.

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