Translation guide
Expresses that something happens or changes with each passing day, or is measured on a daily basis.
Describing how something increases, decreases, or changes as days go by.
A common pattern meaning 'day by day' or 'with each passing day', often used with verbs of change.
Indicating that something is paid, charged, or calculated per day.
Means 'on a daily prorated basis', used for calculating costs, fees, or interest per day.
All three express gradual change over days. 日ごとに is the most neutral and common. 日に日に is slightly more emphatic and often used in spoken language. 日増しに implies a steady increase or intensification and is slightly more literary.
It's getting warmer by the day.
His Japanese is improving by the day.
Literally 'day by day increase', used for gradual intensification, often with adjectives or verbs of change.
It gets colder by the day.
Similar to 日ごとに, emphasizes a noticeable change each day. Often used in spoken Japanese.
He's recovering by the day.
Rent is calculated by the day.
Means 'per day', used for rates, allowances, or quantities.
The parking fee is 2000 yen by the day.
Means 'in units of a day' or 'on a daily basis', used for scheduling or measurement.
You can rent a car by the day.