How Long Do Rats Live in the Wild? Wild Rat Lifespan by Species

Wild rats can carry diseases. Don't touch or handle wild rats or their droppings. For a rat problem in your home, contact a licensed pest professional or your local council. This page gives facts about wild rats; it doesn't give control instructions.

How long do rats live in the wild?

How long do rats live in the wild? Usually less than a year. UC IPM, the University of California's pest management programme, says Norway rats can live up to 18 months, "but most die before they are 1 year old". The Animal Diversity Web gives roof rats about a year in the wild, with 91–97% dying each year, and the AnAge database notes that wild Norway rats rarely live past their first birthday. PetMD sums it up for owners: wild rats typically live less than a year.

That makes the wild rat lifespan a fraction of a pet's. The same species kept as a pet usually lives 2–3 years, and lab rats live 2–3.5 years (Sengupta 2013). The tool above shows the typical and maximum lifespan for each species in the wild, in buildings and in captivity, together with its life cycle and an ID card.

Sewer rat, street rat and city rat lifespan

Sewer rats, street rats and city rats are almost always Norway rats — "sewer rat" and "street rat" are listed names for the species — so the sewer rat lifespan and street rat lifespan are the Norway rat figures: usually under a year, up to about 18 months. City life gives rats plenty of food, but also traffic, poison, cats and fights for space. We found no study that measures city rats' lifespan separately from other wild Norway rats.

Norway rat (brown rat) lifespan

The Norway rat, Rattus norvegicus, is the big, heavy rat of sewers, farms and city streets — and the wild ancestor of every pet and lab rat. The Norway rat lifespan in the wild is short: most die before 1 year, and the longest-lived reach about 18 months (UC IPM), exceptionally 3 years (AnAge). The brown rat lifespan is the same thing, because "brown rat" and "Norway rat" are two names for one species.

In captivity the same species lives far longer. Lab Norway rats live about 2–3.5 years (Sengupta 2013), and the AnAge database records a maximum of 3.8 years, with one calorie-restricted female at 4.6. The Animal Diversity Web's figure of about 2 years in the wild is higher than the university sources, so we show the more cautious UC IPM range.

• Size: head and body 7–9½ in, tail 6–8 in, weight 7–18 oz, up to 20.5 oz (UC IPM). ICWDM gives an average of 12–16 oz.
• Breeding: mature at about 3 months; litters of 6–12 young, born 21–23 days after mating; 3–6 litters a year (ICWDM).
• Home: mostly at ground level and below — burrows, sewers, under slabs and in basements. Cornell IPM notes Norway rats need to drink standing water every day.

Norway rat life cycle

Merck notes that a female rat can quickly become pregnant again after giving birth, so the Norway rat life cycle repeats every couple of months in good conditions. Pups open their eyes at 14–17 days (ADW), start eating solids at 2½–3 weeks and become independent at 3–4 weeks (ICWDM). By about 3 months they can breed themselves. UC IPM says an average female weans 20 or more young a year.

Black rat (roof rat) lifespan and life cycle

The black rat, Rattus rattus, is smaller, sleeker and a far better climber than the Norway rat, with a tail longer than its head and body. The black rat lifespan in the wild is about one year (Animal Diversity Web), with 91–97% of them dying each year. In captivity they can live up to about 4 years (ADW), and AnAge records one that reached 4.2. So how long do black rats live? About a year outdoors, and up to four in captivity.

The roof rat lifespan is the same figure, because "roof rat" is the American name for the black rat. We found no reliable record of the longest-lived wild roof rat.

Black rat life cycle

The black rat life cycle runs at a similar speed to the Norway rat's but with smaller litters. Young are born 21–23 days after mating, in litters of 5–8 (ICWDM). They open their eyes at about 15 days (ADW), may nurse until 4–5 weeks (ICWDM) and are independent and able to breed at about 3 months. Females typically have 3–5 litters a year (UC IPM). Roof rats nest off the ground — in attics, roof spaces, trees and dense plants — and rarely dig burrows (ICWDM).

House rat, garden rat and grey rat: which species are they?

Common names for rats overlap, which causes a lot of confusion. Here is how they map to the two species:

• Brown rat = Norway rat (Rattus norvegicus). Also called the common rat, sewer rat, street rat, wharf rat, Hanover rat and Norwegian rat (Wikipedia), and the grey (gray) rat or barn rat (ICWDM). So how long do grey rats live? Grey rats are Norway rats: usually under a year in the wild.
• Black rat = roof rat = ship rat (Rattus rattus). Also called the house rat, fruit rat and Alexandrine rat (ICWDM; Wikipedia). Despite the name, many black rats are brownish: ICWDM describes brown fur mixed with black, and some forms have grey or white bellies.
• "House rat" is ambiguous. Wikipedia lists it as a name for the black rat, but ICWDM also lists "house rat" among the Norway rat's names. The house rat lifespan is the same either way — about a year or less in the wild — so the lifespan of house rat species isn't much affected by which one you have. Use the tail test below to tell them apart.
• "Garden rat" isn't a species name. We found no authority that defines it. In the UK, the Mammal Society says the brown rat is by far the most common rat, while the black rat is one of the country's rarest mammals, so a rat in a British garden is almost certainly a brown rat. The garden rat lifespan is therefore the brown (Norway) rat's: usually under a year. Where roof rats live, they nest in trees and dense plants and eat fruit and nuts (ICWDM), so they can be garden rats too.
• Ship rat lifespan: "ship rat" is the black rat, which spread around the world on ships — about a year in the wild.

Rat life cycle: from birth to breeding

The rat life cycle is short and fast, which is why rat numbers can climb so quickly. This table compares the two species stage by stage.

How fast do rats breed?

The rat breeding cycle can repeat every couple of months: about three weeks of pregnancy, about three weeks of nursing, and a female can quickly become pregnant again after giving birth (Merck). How many babies do rats have? Norway rats have 6–12 per litter and 3–6 litters a year, so one female can give birth to 18–72 young a year; roof rats have 5–8 per litter and 3–5 litters, or 15–40 a year. The rat gestation period is 21–23 days for both.

The tool above turns those numbers into a "family growth" illustration. Starting with one pair and assuming no deaths, daughters breeding from 3 months and every litter half female, one Norway rat pair could in theory lead to about 288–5,112 rats in a year, and a roof rat pair about 162–1,384. Those are theoretical maximums, not forecasts: in real life most young die, and UC IPM puts the realistic output of a female Norway rat at about 20 weaned young a year.

Norway rat vs roof rat: how to tell them apart

For Norway rat vs roof rat (or brown rat vs black rat), the quickest check is the tail. Cornell IPM's tip: imagine pulling the tail forward over the back — if it reaches past the nose, it's a roof rat; if it doesn't, it's a Norway rat. Here is how to identify rat species in more detail:

Colour is a poor guide: some "black" rats are brown, and Norway rats range from brown to grey. Droppings help when you never see the rat — about ¾ inch with blunt ends for Norway rats, about ½ inch and pointed for roof rats (ICWDM). Where you find them helps too: burrows and ground level suggest Norway rats; attics, roof spaces and trees suggest roof rats.

Why wild rats live much shorter lives than pet rats

Why wild rats die young is no mystery. Pet, lab and wild Norway rats are one species, so the gap between a wild rat's months and a pet rat's years is almost entirely about danger. The main reasons wild rats die young are:

• Predators: cats, owls, dogs and foxes, snakes and other carnivores all hunt rats (Animal Diversity Web). In towns, house cats are the main threat to roof rats.
• Disease and parasites, spread easily in crowded colonies.
• Competition: rats fight for burrows, food and mates, and young rats often lose.
• Weather and hunger: cold, wet winters and food shortages kill many young rats.
• People: traffic, traps and poison.

PetMD lists predation, disease, lack of food and water, and lack of veterinary care as the reasons wild rats live under a year. Remove those, and the same animal lives 2–3 years. For what that longer life looks like, see our pet rat lifespan calculator.

How this wild rat lifespan tool works

Choose a species and where the rat lives. The tool shows the sourced typical and longest lifespan for that combination (UC IPM, ICWDM, Animal Diversity Web, AnAge, Sengupta 2013), the life cycle — pregnancy length, litter size, litters a year and age at maturity — and a species ID card. Where no source measures something, such as rats living in buildings, it says so rather than inventing a number.

The family-growth figure is a simple model: the founding female is mated on day 0; each female gives birth first at maturity (90 days) plus pregnancy (22 days, the middle of 21–23) and then every 365 ÷ litters-per-year days; half of every litter is female; nothing dies. It runs once with the low end of each sourced range and once with the high end, and counts every rat born within 365 days. For Norway rats that gives about 288 (3 litters of 6) to 5,112 (6 litters of 12); for roof rats about 162 to 1,384. Real populations are limited by deaths, food and space.

Frequently asked questions

This calculator gives an estimate for education and fun. Every pet ages differently — for health decisions, talk to your veterinarian.