An extra charge or premium added to a base fee or wage (e.g., overtime premium, late-night surcharge).
深夜勤務は時給の25%割り増しになる。
Night shifts are paid a 25% premium on the hourly wage.
休日出勤は割り増しで支払われることが多い。
Holiday work is often paid with a surcharge.
特急料金にさらに割り増しがある場合もある。
There can sometimes be an additional surcharge on express fares.