Your billing cycle
Day-by-day interest table
| Days | Day count | Balance held | Interest |
|---|---|---|---|
| Days 1-9 | 9 | $3,000 | $18.49 |
| Days 10-19 | 10 | $3,400 | $23.28 |
| Days 20-30 | 11 | $2,800 | $21.09 |
| Total for the cycle | $62.85 | ||
Your billing cycle breakdown
Your billing cycle interest
Starting balance $3,000 at 24.99% APR over a 30-day cycle. Average daily balance: $3,060. Daily periodic rate: 0.0685%.
This cycle's interest charge (average daily balance method): $62.85.
Segment-by-segment breakdown
• Days 1-9 (9 days) at $3,000: $18.49 interest.
• Days 10-19 (10 days) at $3,400: $23.28 interest.
• Days 20-30 (11 days) at $2,800: $21.09 interest.
How this compares to the simplified monthly model
The balance × APR÷12 model most calculators use would estimate $63.72 for this same average balance - a difference of $0.87 more than the daily-accrual figure. The gap grows when a balance swings a lot mid-cycle from new purchases or a large payment.
Cutting this charge
• Pay as early in the cycle as possible - every day sooner a payment posts is a day less balance accruing interest.
• Avoid new purchases on a card carrying a balance - most issuers apply interest to new spending immediately once a balance is being carried, with no grace period.
• Paying in full by the due date each cycle avoids this charge entirely going forward - see the Credit Card Payoff Calculator for a full elimination plan.
How the daily interest calculator works
Most US credit card issuers don't wait until the end of the month to charge interest - they accrue it daily against your average daily balance, then bill the total once per statement. This calculator splits your billing cycle into segments at each purchase or payment you add: every segment holds a constant balance for a certain number of days, and interest for that segment is balance × (APR ÷ 365) × days. Summing every segment gives the cycle's real interest charge - the same method your issuer's statement uses, not a flattened approximation.
The day-by-day table exists because that's the only way to see where the charge actually comes from: a large balance held for many days contributes far more than the same balance held briefly. It's also why paying early in the cycle matters more than paying the same amount later - every day sooner a payment posts is a day of interest that never accrues. The comparison to the simplified balance × APR÷12 monthly model (used by the payoff calculator elsewhere on this site) shows how close that approximation usually is, and when it starts to drift - mainly when a balance swings a lot mid-cycle.
Statement credits and refunds work the same way as a payment in this model - both reduce the balance for the segment they land in, which is why returning a purchase mid-cycle saves less interest than never making it, but still saves something from the day the credit posts forward. Multiple purchases or payments on the same day simply net together into a single balance change; the segment boundaries only move where the running balance actually changes, not on every calendar day.
Frequently asked questions
- Is daily or monthly interest accrual more accurate for my card?
- Daily accrual against the average daily balance is what most major US issuers actually use - check your cardholder agreement's "How We Calculate Interest" section to confirm. Monthly accrual (balance × APR ÷ 12) is a simplification that's usually close, but can undershoot the real charge if your balance changed a lot mid-cycle.
- Why does a mid-cycle purchase increase my interest so much?
- Because it raises your balance for every remaining day in the cycle, not just the day it happened. A $500 purchase on day 5 of a 30-day cycle accrues interest against that extra $500 for 25 days - the earlier in the cycle a purchase lands, the more it costs in interest.
- How do I avoid daily interest accrual entirely?
- Pay your statement balance in full by the due date every cycle. Most cards offer a grace period on new purchases - but only if the previous statement was paid in full. Once a balance carries over, new purchases typically start accruing interest immediately with no grace period.
- Why is the interest slightly different from a flat balance × APR ÷ 365 × days estimate?
- Because your balance rarely stays perfectly flat for the whole cycle - a purchase or payment changes it partway through. This calculator accounts for that by splitting the cycle into segments at each event, which a single flat-balance estimate can't do.
- Does a shorter billing cycle mean less interest?
- Not by itself - fewer days means fewer days of accrual on the same balance, but issuers also bill more often, so the annual total is similar. What actually changes the yearly cost is your average balance and APR, not the cycle length in isolation.