A betta is a small fish with a very small stomach, so the amount of food matters more than most new keepers expect. Overfeeding is the most common feeding mistake with bettas, and it causes two problems at once: the fish eats more than it can digest, and the leftover food rots in the tank and pollutes the water. This calculator gives you a simple daily pellet count based on the size of your betta, plus a weekly table that includes a fasting day.
Bettas are often sold in tiny cups with little guidance about feeding, which is why so many owners guess. A common guess is a large pinch of food, but a betta stomach is roughly the size of its eye. That image helps you understand why two to five small pellets per day is usually enough. More food does not make a betta grow faster or healthier. It mostly makes the water dirtier and the fish bloated.
To use the calculator, measure or estimate the body length of your betta in centimetres, not counting the tail fin. Tail fins vary a lot between betta types, so body length is a fairer measure of size. Enter that number and press the button. The tool returns a daily pellet count and splits it into a morning meal and an evening meal. Splitting the food helps digestion and gives you a second chance each day to watch how eagerly your fish eats.
The weekly table shows the same pellet count for six days and zero on the seventh day. That fasting day is deliberate. In the wild, bettas do not eat a full meal every single day, and a regular fast gives the digestive system a rest. Many experienced keepers fast their bettas one day per week. If your betta looks thin or is recovering from illness, skip the fast until it is eating well again and looking stronger.
Here is a worked example. A betta with a body length of four centimetres gets four pellets per day in this calculator, split as two in the morning and two in the evening. A smaller betta of two centimetres gets two pellets per day, one at each meal. A large betta of five centimetres or more gets five pellets per day, split as two and three. These are starting points, not rigid rules, so watch your fish and adjust by one pellet if needed.
Pellet size changes everything, so check the pellets you actually use. Some brands make tiny micro pellets and others make larger ones. If your pellets are much bigger than average, feed one fewer per day. If they are very small, you may need one more. Soak dry pellets briefly before feeding if your betta often spits them out, because a soaked pellet is softer and easier to swallow. Never feed a pile of pellets at once, even if the total count is right.
Watch for signs of overfeeding over the first two weeks. A bloated belly, a curved spine shape after eating, long stringy waste, or uneaten pellets sitting on the gravel all point to too much food. Cloudy water and a sudden algae bloom can also follow overfeeding, because the extra nutrients feed algae. If you see these signs, cut back by one pellet per day and remove any uneaten food after two minutes with a small net or a turkey baster.
Signs of underfeeding are different and slower to appear. A betta that is too thin will show a pinched belly and a head that looks large compared with its body. It may also become less active and lose colour. If you see this, add one pellet per day and check the water quality too, because poor water can reduce appetite. A fish that refuses food for more than three days may be ill or stressed, and that needs attention beyond feeding.
Feeding and water quality are closely linked in a small betta tank. Most bettas live in tanks of twenty litres or less, so a few uneaten pellets can quickly raise ammonia. Test the water weekly if you can, and change part of the water on a regular schedule. A clean tank makes feeding simpler, because a healthy betta in clean water usually eats eagerly and digests well. If the water is dirty, even the right amount of food can cause problems.
Variety helps, but it does not replace a sensible staple. You can offer frozen bloodworms or brine shrimp once or twice a week as a treat, replacing one pellet meal on that day rather than adding extra food on top. Live foods should come from a trusted source only. Avoid feeding human food, bread, or flakes made for large community fish, because these are not sized or balanced for a betta and they foul the water faster.