Having brittle nails is very frustrating, you cannot even do your manicure without breaking a nail. It may be possible that your calcium intake is low so drink 2 glasses of milk everyday. It may also caused by the lack of water in the body so drink adequate fluids.
The most common thing that makes you nails brittle are harsh detergents and water, which can stress nail fibers. So be sure to put rubber gloves on while you clean or do dishes.
Also, avoid using perfume lotions that usually contain alcohol if your nails are brittle. It will only make your nails worse.
Do not bite your nails. It damages the nails and cuticles, causing deformation and uneven nail growth.