increment; amount of increase
A technical or formal noun used in contexts such as statistics, economics, and science to refer to the quantity by which something increases.
The amount of increase in last month's sales exceeded expectations.
This graph shows the increment in population.
増分 is a near-synonym also meaning 'increment', but 増加量 is more common in formal reports and statistics.
Compound of 増加 (increase) and 量 (amount, quantity).