Betta looks give a rough age only. Little colour or fin shape means under about 3 months; developing colour and fins, about 3–5 months; full size, fins and colour, an adult of 5 months or more (Animal Diversity Web). Gradual fading and ragged fins can mean old age (3 years +) — or illness.
General information only. Vets publish few betta figures, so we combine vet, university, database and peer-reviewed sources and say which is which; pet-care sites are used only to fill gaps. For a sick or injured betta, see an aquatic (fish) vet. We give no medication advice.
How old is my betta? What its looks can tell you
"How old is my betta?" is hard to answer exactly — no published chart links a betta's looks to its precise age. What the sources do give is a sequence: young bettas have little colour or fin shape until about three months, sexes become clear soon after, and bettas are sexually mature at around five months (Animal Diversity Web). After that, an adult's appearance stays much the same for years, until slow changes in old age.
So looks tell you three things reliably: whether your betta is very young, still growing or adult. Within adulthood, they tell you very little. The estimator above combines size, fins, colour and activity, then gives a rough range and a confidence level — high when the cards agree, low when they don't or when they point to old age, because the same signs can mean illness.
Betta fish age chart
This betta fish age chart is our summary of the published timings. It's a guide to stages, not a ruler: growth depends on food, temperature and space, and fin length depends on the type of betta. PetMD gives an adult body length of 2.5–3 inches, and FishBase lists a maximum total length of 6.5 cm for the species.
| Age | Size | Fins | Colour | Source |
|---|---|---|---|---|
| 0–2 days | Egg in the bubble nest | — | — | ADW: hatch at 24–48 h |
| Up to ~3 months | Tiny to small fry | Short, plain | Pale or brownish | ADW; UF/IFAS |
| ~3–5 months | Half to near adult size | Filling out; males longer | Colour coming in | ADW (sexing easy from ~3 months) |
| 5 months – 3 years | Full size: body 2.5–3 in | Full for its type | Bright and even | ADW (mature ~5 months); PetMD (size) |
| 3 years + | Full size, may thin | Tips may fray or curl | May fade slowly | Hepper (vet-reviewed; gap fill) |
Note two traps. Females naturally have shorter fins than males, and short-finned types such as plakats keep short fins all their lives — so short fins alone don't mean a young fish. And colour can fade from stress, cold water or illness at any age (Unusual Pet Vets).
Betta fish life cycle: egg to older adult
The betta fish life cycle starts at the water's surface. Bettas evolved in warm, low-oxygen water, and UF/IFAS explains that the bubble nest keeps eggs near the surface where oxygen exchange is better, while also stopping them drying out. The male does almost all the parenting.
| Stage | When | What happens |
|---|---|---|
| 1. Bubble nest and spawning | Day 0 | The male builds a nest of bubbles; about 300 eggs are laid in one spawning, and the male collects them into the nest (UF/IFAS). |
| 2. Egg | 24–48 hours | The male guards the nest until the eggs hatch, sooner in warmer water (ADW). |
| 3. Larva / fry | About 3 days after hatching | The larvae live on their yolk sacs, then swim free and start eating tiny live food such as infusoria and brine shrimp (UF/IFAS). |
| 4. Juvenile | About 3 months | Colour and fin shape appear and sexes become easy to tell; farms separate males at 3–4 months (ADW; UF/IFAS). |
| 5. Adult | About 5 months | Sexual maturity (ADW). Most bettas are sold as young adults, often 6–12 months old (Chewy). |
| 6. Older adult | About 3 years + | The start of the typical 3–5 year lifespan (PetMD). Fertility falls with age (AnAge). |
Fry are tiny and need live food at first; UF/IFAS lists brine shrimp nauplii, microworms and other small organisms, moving to flakes or pellets as the fish grow. In the wild, the breeding season in Thailand falls in April and May, when bettas move to shallow edges to spawn (UF/IFAS).
Signs of an older betta — and when it's illness instead
Hepper's vet-reviewed guide describes old-age changes as gradual, over several months: duller or slightly brownish colour, ragged fins whose ends may curl, more sleep, less flaring and sometimes weight loss even when the appetite is normal. An older betta usually shows only some of these, not all at once.
The catch is that Unusual Pet Vets list nearly the same signs — loss of bright colour, thin or uneven fins, weight loss and not eating — as signs of illness. The difference is speed. Changes over a few days point to a problem with the water or health, not age. Check the temperature and ammonia first (PetMD), and see an aquatic vet if the fish stops eating, clamps its fins or develops spots or patches.
How old is my betta fish if I know when I bought it?
Then you can do much better than looks. "How old is my betta fish?" becomes a sum: the age when you bought it plus the time you've had it. Shop bettas are often 6–12 months old when sold (Chewy), so a fish you've had for two years is probably 2.5–3 years old. Our age-at-purchase calculator does the sum for you, and the betta fish lifespan calculator shows how much of a typical life that is.
How this betta age estimator works
Pick at least two cards. Size, fins and colour only develop with age, so any card that points to a young fish takes priority. If all the cards look adult, the result is "adult — 5 months or older"; if two or more point to old age, it's "possibly older — about 3 years +", always with low confidence, because illness looks similar. The estimator never claims a precise age.
Frequently asked questions
How can I tell how old my betta is?
Only roughly from its looks. Little colour or fin shape means under about 3 months; colour and fins developing means about 3–5 months; full size, fins and colour means an adult of 5 months or more (Animal Diversity Web).
At what age is a betta fully grown?
Bettas are sexually mature at around 5 months (ADW). Adults reach a body length of about 2.5–3 inches (PetMD).
When do betta fry get their colour?
From about three months old. Before that they show very little colour or fin shape (Animal Diversity Web).
How long do betta eggs take to hatch?
24–48 hours after spawning, depending on water temperature (Animal Diversity Web).
When do betta fry start swimming?
After they've used up their yolk sacs, about 3 days after hatching (UF/IFAS).
What are the stages of the betta fish life cycle?
Bubble nest and spawning, egg (24–48 h), fry (from hatching), juvenile (about 3 months), adult (about 5 months) and older adult (about 3 years +).
Does a faded betta mean it's old?
Not necessarily. Gradual fading over months can be age (Hepper), but faded colour is also a sign of illness (Unusual Pet Vets). Check the water and see a vet if the change is quick.
Can you tell a betta's age by its fins?
Only partly. Fins develop from about 3 months, but females and short-finned types have short fins as adults, and fin damage can happen at any age.
How big is a 1 year old betta?
Full adult size — about 2.5–3 inches of body (PetMD). Bettas stop changing much once mature, so size can't separate a 1-year-old from a 2-year-old.
This calculator gives an estimate for education and fun. Every pet ages differently — for health decisions, talk to your veterinarian.