The plural of half is halves.
One of two parts, equal in size to the other, which together make a whole.
Most English nouns ending in the letter -f do not adhere to standard English for forming plurals. They have an irregular plural form and replace the f with -ves.
The word half follows this same pattern, and so the plural of half is halves.
This is in contrast to the plural of hoof, which can be written in two different ways as hoofs or hooves.
As the English language is one which has gradually formed with input from many other languages, its rules can often feel arbitrary!
Singular Example: John Lennon was one half of the Beatles' famous songwriter duos, his partner being Paul McCartney.
Plural Example: As the popular British phrase goes 'Football (soccer) is a game of two halves'.
The graph shows the occurances of the plural of half in written English since 1800 using Google's Ngram Viewer.
In Chinese philosophy, the symbol for yin and yang is two halves of a circle divided by a curved line. Each half representing complementary universal forces.