01How Much Interest Am I Paying Each Day?
The short answer: on most UK credit cards your daily interest is the APR divided by 365, applied to the balance you carried at the end of yesterday. So a typical card quietly costs you a few pounds a day that never appears as its own number on your statement.
Open your last credit card statement and look at the summary box. APR is there. So is the interest you were charged this month. On some cards you'll see the average daily balance the lender used to calculate it.
The maths is daily. The presentation is monthly. That's not a conspiracy, it's the regulated format. Statements run on a monthly cycle because billing does. The figure you'd actually find useful, what today is costing you, is buried in the inputs and never spelled out as a number on its own.
02What it works out to
For most UK credit cards, it's the APR divided by 365, applied to the balance you were carrying at the end of yesterday.
A £3,000 card at 24.9% APR is about £2.05 a day. Five debts averaging 22% APR on £18,000 of balance is about £11 a day. £77 a week. None of that is new information. It's just not anywhere you'd look at it.
If you want the full picture of how that APR is set and what it costs over a year, see credit card APR explained.
03So we put it on the front of the dashboard
We added a tile to TrySnowball called Interest Burn. APR × balance ÷ 365, in pounds and pence per day, updated whenever a balance changes.
£8.42 today. Right now, today. Every day you wait, this gets added.
The yearly figure is the one people argue with. The daily figure is harder to wave off.
04What changes
When the cost is daily, the response can be too. The £30 you didn't spend on Saturday lands on the focus debt on Monday. Tomorrow's figure is a bit lower than today's. Across a year, days like that compound into a different debt-free date.
The work is small, repeated, and a bit boring.