zmniejszyć się o połowę in English:

we halved the price

if something halves, it is reduced by half

Due to strict environmental laws, pollution levels have been halved.

The industry's rush of consolidation in the last decade nearly halved the number of banks in the U.S. to around 7,500.; The potatoes will cook more quickly if you halve them before you put them in the oven; Their profits have halved in the last six months

In our monogamous part of the world, to marry means to halve one’s rights and double one's duties.