👯 Pets That Should Never Live Alone — and What a Pair Really Costs

Here is a cost that almost no pet-care page tells you about up front: for a lot of popular small pets, the correct number to buy is two. Not because two is nicer, but because one is a welfare problem — and in some countries, a legal one.

We rated all 45 pets on this site for whether they need company of their own species. 19 of them do. Below is the full list with the real monthly cost of keeping them properly, so nothing surprises you at the checkout.

The 19 pets that shouldn't live alone

Costs are per animal per month. Where a pet carries a ×N minimum tag, that is the smallest group it should be kept in, and the monthly bill genuinely multiplies by it.

Pet	Group size	Cost per animal	What you actually pay
Hissing Cockroach	Pair or group	$5–$15/mo	Same tank, same bill
Shrimp & Snails	Pair or group	$8–$20/mo	Same tank, same bill
Hermit Crab	Pair or group	$10–$25/mo	Same tank, same bill
Mouse	×2 minimum	$8–$18/mo	$16–$36/mo
Goldfish	Pair or group	$15–$40/mo	Same tank, same bill
Gerbil	×2 minimum	$10–$20/mo	$20–$40/mo
Rat	×2 minimum	$15–$30/mo	$30–$60/mo
Parakeet & Small Birds	×2 minimum	$15–$35/mo	$30–$70/mo
Guinea Pig	×2 minimum	$25–$45/mo	$50–$90/mo
Chinchilla	×2 minimum	$25–$50/mo	$50–$100/mo
Quail	×3 minimum	$15–$35/mo	$45–$105/mo
Rabbit	×2 minimum	$30–$60/mo	$60–$120/mo
Sugar Glider	×2 minimum	$30–$60/mo	$60–$120/mo
Chicken	×3 minimum	$20–$45/mo	$60–$135/mo
Ferret	×2 minimum	$40–$80/mo	$80–$160/mo
Duck	×3 minimum	$25–$55/mo	$75–$165/mo
Goat	×2 minimum	$40–$90/mo	$80–$180/mo
Mini Pig	×2 minimum	$50–$120/mo	$100–$240/mo
Pony	×2 minimum	$150–$400/mo	$300–$800/mo

In Switzerland, some of these are illegal to keep alone

Switzerland is unusual in writing this into law. Article 13 of its Animal Protection Ordinance names species that may not be kept singly, and the list is a good sanity check on your own plans: guinea pigs, mice, gerbils, rats, degus, chinchillas, ferrets, budgies, lovebirds, parakeets, parrots, macaws, cockatoos, canaries, finches, Japanese quail — and goldfish.

Two things stand out. The first is that a goldfish is on it, which surprises nearly everyone; goldfish are sociable animals and the lone fish in a bowl is a genuinely poor life. The second is who is not on it: the Syrian hamster, which Swiss regulations explicitly describe as a loner that should be kept alone. Sociability is a fact about the species, not a general rule about kindness.

When a friend doubles the bill — and when it doesn't

This is the distinction that matters for your budget, and it splits the list cleanly in two.

Animals that eat, drink, and see a vet individually really do cost twice as much in a pair. Two guinea pigs eat two guinea pigs' worth of hay and pellets and need two guinea pigs' worth of vet care. The same goes for rabbits, rats, mice, gerbils, chinchillas, ferrets, sugar gliders, and budgies. For chickens, ducks, and quail the practical floor is three, not two, so the multiplier is bigger again.

Tank and colony species are the happy exception. Goldfish, shrimp and snails, hermit crabs, and hissing cockroaches all share one tank, one bin, one heater, and one bag of food. Their monthly figure already covers the group, so a second animal costs almost nothing to run. What it does cost is space: a second goldfish wants roughly another 10 gallons of water, and that is a one-off tank purchase rather than a monthly bill.

One thing the monthly figure never doubles is housing. A bonded pair shares a cage — they need a bigger cage than a single animal, not two cages. Our setup cost guide covers that side of it.

The pets that are genuinely happier alone

If your budget or your space really only stretches to one animal, do not compromise by getting one of the social species. Get a solitary one instead. Genuinely solitary pets include the Syrian hamster, the betta fish (two males will fight to the death), the hedgehog, and most reptiles — geckos, bearded dragons, snakes, chameleons — along with tarantulas, scorpions, praying mantises, and crayfish, several of which will simply eat a tankmate. A single pet from this list is a better pet than a lonely one from the list above.

You can't just add a second one

The last thing worth knowing is that pairing is a process, not a purchase. Small social mammals are territorial about their own space, so two adults introduced by dropping one into the other's cage will usually fight. The standard approach is neutral territory, short supervised sessions, over days or weeks, and even then not every pairing takes — same-sex pairs of siblings are the easiest, and unneutered mixed pairs will simply give you babies.

There is a shortcut, and it is the best advice on this page: adopt an already-bonded pair from a rescue. Guinea pigs, rabbits, and rats all turn up in rescues in bonded pairs, the hard part is already done, and it is almost always cheaper than two animals from a shop. Our adopt, don't shop guide has more on finding one.

Work out what fits

The Pet Finder has filters for both sides of this: "needs a friend" if you like the idea of a pair, and "happy on its own" if one is all you have room for. Costs on every pet page already show the ×N minimum, so the number you see is the number you pay. You can also take the free pet quiz or compare the running costs of all 45 pets in how much do pets cost.

🛒 Recommended supplies

Hand-picked gear for this guide. Affiliate links — we may earn a commission. The $/$$/$$$ badges are a rough budget guide, not live prices.

❓ Common questions