The confectionery giant's flagship brand, made in York, will see a "small" sugar reduction in the reformulation being introduced across the KitKat milk chocolate range.
Nestle said it would cut more than 1,000 tonnes of sugar and three billion calories from the UK's diet.
Crucially for consumers, there will be no change to the recommended retail price or size of the bar, which will be launched in updated packaging saying "Extra Milk & Cocoa".
Earlier this month, Nestle announced that it would reduce sugar by 10% across its confectionery portfolio by 2018 through a range of methods including reformulation.
Fiona Kendrick, chairwoman and chief executive of Nestle UK and Ireland, said: "When we announced that we were removing some of the sugar from our confectionery, the first questions that consumers asked us were 'Are you going to make things smaller?' and 'Will it taste the same?'"
"I'm pleased to say that these products are the same size as the ones they are replacing and taste just as good.
"Milk and cocoa has formed the basis of the KitKat recipe ever since it was introduced in 1936 so, while people might have been expecting us to add something else, this is a great example of us using our strength in research and innovation to develop a great recipe that replaces sugar with a bit more of the existing, natural ingredients that people know and love."