A reintroduction that works is 4 stages spread over 2 weeks, and the number that decides the outcome is 10 cm: the gap at which 2 cats eat with another cat's face in view and no barrier between the noses. Move faster and you get a 5-second fight; move slower and you spend 6 months with 2 cats living on separate floors.
Why the gate is 10 cm, not 30
Distance changes the job. At 2 m a cat can break eye contact by turning its head 20 degrees and still eat, so a 2 m session rehearses avoidance rather than tolerance. At 10 cm there is nowhere to look, and the cat has to hold position while another cat chews 1 m from its own bowl. That is the skill the rest of the year depends on: passing in a 90 cm hallway, sharing a 1.5 m window ledge, waiting 30 seconds for a litter box. A 30 cm gap is the worst of both, close enough to trigger a swat and far enough that the swat lands in air and teaches nothing.
Stage 1, days 1 to 3: scent, no sight
Door closed, no crack, no gate. Swap bedding every 12 hours so each cat sleeps in the other's smell, and brush both cats with the same brush in the same session. Feed 2 meals a day on opposite sides of the door, 1 m back on each side, and put the bowls down within 30 seconds of each other. If either cat stops eating, walks off, or paws the door for more than 20 seconds, move both bowls 50 cm further out and repeat the day. Stage 1 is done when both cats eat 2 consecutive meals at 1 m with no pawing at the door.
Stage 2, days 4 to 6: a 10 cm crack
Wedge the door open 10 cm, or use a gate with a 10 cm gap at the bottom, and pin a towel across the lower 20 cm so no paw fits through. Three sessions a day of 8 to 10 minutes, bowls at 1.5 m, closing to 80 cm by day 6. End every session while both cats are still eating, and end it early if you hear the first hiss: a hiss at second 40 means the next session starts at 60 cm, not 80. No toys in the room, no person between the cats, and never pick 1 up to show it the other.
Stage 3, days 7 to 10: the 10 cm threshold
A 120 cm mesh gate, floor to top, so neither cat can go over or under, and bowls slid in until the rims sit 10 cm from the mesh on each side. Two sessions of 10 minutes a day. The pass rule is 3 consecutive sessions in which both cats eat at 10 cm, ears forward or neutral, tail down or level, and no hiss, growl, or paw through the mesh. One flinch resets the count to zero; you hold this stage for another 48 hours rather than dropping back to stage 2, because the cats are close and only the last 40 cm is missing.
Stage 4, days 11 to 14: same room
Harness and a 1.2 m leash on the more reactive cat, and a second person on the other if you have one. Start 2 m apart, 5 minutes, twice a day, and climb 5, 10, 20, 30 minutes across 4 days. Put a food puzzle down at minute 3 so the cats have a job that is not each other. Close the distance by 30 cm per session only if both cats keep eating and neither holds a stare longer than 3 seconds. After 72 hours with no swat, no chase, and no blocked doorway, leave the connecting door open overnight and keep 1 litter box in each half of the house for another 30 days.
The 4 stages at a glance
| Stage | Days | Barrier | Distance | Session | Pass rule |
|---|---|---|---|---|---|
| 1 scent | 1 to 3 | closed door | 1 m each side | 2 meals a day, 10 min | 2 meals at 1 m, no pawing |
| 2 sound and smell | 4 to 6 | 10 cm crack, towel to 20 cm | 1.5 m down to 80 cm | 3 x 8 to 10 min | eats at 80 cm, no hiss |
| 3 sight at 10 cm | 7 to 10 | 120 cm mesh gate | 10 cm at the bowl | 2 x 10 min | 3 sessions at 10 cm, ears forward |
| 4 same room | 11 to 14 | none, harness and 1.2 m leash | 2 m down to 30 cm | 5 to 30 min, twice a day | 30 min, no stare over 3 s |
Total elapsed time is 14 days per attempt, and most households need 1 to 3 days of slack, so plan for 17 days.
Reset rules, and what a second failure means
A swat, a charge, or a 5-second grapple sends you back exactly 1 stage for 48 hours, never to day 1: Two failed attempts at stage 2 mean 5 days parked at stage 1 with 2 bedding swaps a day, then a vet check before you try the crack again. Three failures at the same stage mean the house needs permanent separate zones, 2 litter boxes per zone, and a behavior consult, because 2 more weeks of gates will not change their answer.
Fix the resources before stage 4
Face-to-face time fails when the room behind it is under-supplied. For 2 cats: 3 litter boxes at 60 cm or longer, 3 water bowls 1 m from the food, 2 feeding stations at least 2 m apart and out of sight of each other, 2 perches at 1.2 m or higher, 1 vertical scratch post 80 cm tall, and 1 hiding box per cat with 2 exits. Add 1 of each before stage 4, not after the first fight, and check that no single cat can guard 2 resources from 1 spot; a 90 cm hallway that both cats must use is a guard point no gate can fix. The resource layout that supports this is spelled out in the multi-cat hierarchy guide.
When to call a behaviorist
Stop the plan and book a consult if 2 Class 3 events land inside 7 days, if any bite breaks skin on a cat or a person, if you have not reached stage 3 after 3 weeks of daily work, or if 1 cat stops eating for 24 hours or hides more than 20 hours a day. A veterinary behaviorist can also assess whether 2 to 6 weeks of medication is worth it to get arousal low enough for stage 3 to hold, and can rule out pain and thyroid disease that make a cat react at 10 cm. If the fights started over a doorway, a bowl, or a lap, the mechanics are in multi-cat conflict; the breed quiz helps if the 2 cats differ a lot in size and tempo.
Five steps to start tonight
- Close the door and swap bedding every 12 hours for 3 days.
- Feed 2 meals a day at 1 m on each side, bowls down within 30 seconds.
- Open a 10 cm crack on day 4, towel across the bottom 20 cm.
- Hold stage 3 until 3 consecutive meals happen at 10 cm with ears forward.
- Add 1 litter box, 1 bowl, and 1 perch before the first same-room session.
Frequently asked
How long does a multi-cat reintroduction take?
Fourteen days across 4 stages, plus 1 to 3 days of slack, so plan on 17 days of doors. Stage 1 is days 1 to 3, stage 2 is days 4 to 6, stage 3 is days 7 to 10 at a 10 cm gate, and stage 4 is days 11 to 14 in the same room from 5 to 30 minutes.
Why does the gate have to be 10 cm?
Because at 10 cm a cat cannot look away and still eat, so it rehearses the skill it needs for a 90 cm hallway or a shared window ledge. At 2 m the cat just turns its head 20 degrees and avoids the problem, and a 30 cm gap is close enough to trigger a swat and far enough that the swat teaches nothing.
What counts as failing a stage?
A hiss, a swat through the mesh, a charge at the gate, or a cat that stops eating resets the count to zero. Hold the same stage another 48 hours and drop the distance by 30 cm. A swat or a 5-second grapple means going back exactly 1 stage for 48 hours, never back to day 1.