Irish Calculators
Loans & mortgages

Line of Credit Daily Interest Calculator

Reconstruct interest and closing debt over a statement period from your entered transactions. The tool does not infer future minimum payments, rate changes or capitalised statement charges.

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Your numbers

Date, signed amount. Positive = drawdown; negative = principal repayment. Changes apply at the start of the stated date. Leave blank if there were no transactions.
%
Simple daily interest uses the annual rate divided by the chosen day-count denominator (365 or 360). This is not a fee-inclusive APR.
Your figures stay on this device.

How the calculation works

Reconstruct simple daily line-of-credit interest from opening debt and dated drawdowns or principal repayments. Closing principal is shown separately from interest and fees, so the output does not silently capitalise those charges.

Accrue simple daily interest on the previous balance until each event; apply the drawdown or repayment, then accrue to the exclusive statement end.

  1. Start from known principal

    Use debt owed at the opening date. Include previously capitalised charges only if they already form part of that known principal balance.

  2. Accrue between events

    Charge simple interest on the previous balance until each event date. Apply the drawdown or principal repayment, then continue with the changed balance from that date.

  3. Reconcile the end position

    Accrue after the final event to the exclusive statement end. Report closing principal and add separate fees to interest without increasing that principal automatically.

Worked example: Repayment changes the next five days

Sample inputs demonstrate the method. They are not a forecast or product offer.

Debt of €1,000 accrues €1 daily for five days. A €500 repayment on 6 January reduces the next five days to €0.50 each. Interest is €7.50 and principal closes at €500. Adding €2 fees gives €9.50 due separately.

Opening debt
1000
Opening date
2026-01-01
Statement end date (exclusive)
2026-01-11
Dated drawdowns and repayments
2026-01-06,-500
Annual nominal interest rate (%)
36.5
Credit limit
2000
Day-count denominator
Actual days / 365
Separate statement fees
2

Expected result

Closing principal
€500.00
Accrued interest
€7.50
Interest and fees due separately
€9.50
Worked example: Drawdown at opening and repayment at end boundary

Sample inputs demonstrate the method. They are not a forecast or product offer.

Opening debt
0
Opening date
2026-01-01
Statement end date (exclusive)
2026-01-11
Dated drawdowns and repayments
2026-01-01,1000 2026-01-10,-1000
Annual nominal interest rate (%)
36.5
Credit limit
1000
Day-count denominator
Actual days / 365
Separate statement fees
0

Expected result

Closing principal
€0.00
Accrued interest
€9.00

Understanding your result

Earlier repayments reduce the balance for more interest days. An identical repayment near statement end leaves the higher debt outstanding longer and therefore costs more under these assumptions.

The calculation assumes a constant rate and simple accrual. It does not allocate a cash payment between interest, fees and principal or model automatic interest capitalisation.

Questions you might have

Why use an exclusive end date?

A period from 1 January to 2 January contains one interest day. This avoids counting a boundary day twice.

Choosing the right inputs

Dated drawdowns and repayments
Enter date,signed amount per row. Positive means drawdown and negative means principal repayment. Changes apply at the start of that date; leave blank when there are none.
Statement end date (exclusive)
Use an exclusive statement end date. That boundary day is not another interest day, avoiding double counting across adjoining statements.
Day-count denominator
Choose the contractual denominator, 365 or 360. Actual days are counted, using the annual nominal rate divided by that denominator.
Credit limit
Supply the applicable credit limit. The model does not approve additional borrowing or raise the limit automatically.

Common mistakes to avoid

  • Do not enter a full cash payment as principal repayment if part settled charges.
  • Do not reverse transaction signs or include the exclusive end as an extra interest day.

Assumptions to check

  • No automatic credit-limit increase, rate changes or compound statement charges.

Sources and method

Read our calculation and testing approach.