Margin Interest Calculator
Estimate simple margin interest from a borrowed USD balance, a user entered annual rate, a selected day count basis, and a holding period.
How it works
Enter the borrowed balance in USD, the annual rate as a percentage, and the number of days. Select a 360 or 365 day calculation basis. The rate is the assumption you enter, not a rate fetched from a brokerage.
The calculator estimates daily simple interest, interest for the selected period, a 30 day illustration, and an annual equivalent using the selected day count. It also divides period interest by the borrowed balance to show the interest only break even percentage.
For a USD 10,000 balance at 12% for 30 days on a 360 day basis, daily interest is about USD 3.333333 before display rounding and the period estimate is USD 100. On a 365 day basis, the 30 day estimate is about USD 98.63. The annual equivalent is USD 1,200 on either basis when the balance and rate stay constant.
Use the result as a scenario estimate. Confirm the applicable currency, balance, rate schedule, day count, and accrual terms with your brokerage statement. Interest and fees may be calculated differently by account or currency.
Step by step
- Enter the borrowed balance, annual rate, and days.
- Choose the day count basis used for the estimate.
- Review daily, period, 30 day, annual, and break even figures.
Worked example
For a USD 10,000 borrowed balance, a 12% annual rate, 30 days, and a 360 day basis, daily interest is about USD 3.333333 before display rounding. The estimated 30 day interest is USD 100.
The 30 day interest illustration is USD 100, and the annual equivalent is USD 1,200 if the balance and rate stay constant. Interest divided by the borrowed balance is 1% for this period. These values are verified by the calculation test.
When to use this calculator
Use this calculator to estimate simple interest for a user supplied rate and a constant borrowed balance over a chosen period.
Use a statement or account terms for the actual rate, accrual basis, and amount owed. This calculator does not retrieve brokerage rates or model the complete account bill.
Common input mistakes
Do not treat the selected 360 or 365 day basis as universal broker policy. Do not assume the monthly illustration is a calendar bill. Enter the balance and rate for the same currency and confirm the applicable terms.
Do not interpret the break even percentage as a required return on total account equity. It compares modeled interest with the borrowed balance and excludes fees, taxes, price changes, and other costs.
Formula
dailyRate = (annualRate / 100) / dayCount
dailyInterest = borrowedBalance × dailyRate
periodInterest = dailyInterest × holdingDays
30 day illustration = dailyInterest × 30
annual equivalent = dailyInterest × dayCount
breakEvenPct = periodInterest / borrowedBalance × 100
If borrowedBalance is zero, breakEvenPct is unavailable because the denominator is zero.
The calculation uses a constant balance and rate without compounding. The annual equivalent spans the selected 360 or 365 day basis. Amounts are displayed in USD and no currency conversion is performed.
Assumptions and limits
This is a simple interest estimate with a constant borrowed balance and annual rate. It does not model compounding, changing balances, rate tiers, broker fees, collateral rules, taxes, currency conversion, or the exact accrual method on an account statement. The 30 day amount is an illustration, not a calendar bill. Confirm the applicable rate and day count for the relevant currency and account. Results are not a broker quote or borrowing recommendation.
Key terms
- Simple interest estimate
- Simple interest calculated from a constant borrowed balance, a user supplied annual rate, a selected day count basis, and a number of days.
- Day count basis
- The selected divisor of 360 or 365 used to convert an annual rate to a daily rate.
- Interest break even percentage
- Estimated period interest divided by the borrowed balance. It covers interest alone and is not a required return on total account equity.
Related tools
Use Option Breakeven to examine an option's expiration threshold, or Margin Call Calculator to estimate a separate maintenance scenario. Neither tool supplies a broker interest rate.
The interest estimate here uses a constant borrowed balance and a user entered rate. Check your brokerage statement for the applicable balance, currency, rate schedule, and accrual terms.
FAQ
Can I estimate one day of interest?
Yes. Set the holding period to one day. The estimate uses the entered balance and annual rate divided by the selected 360 or 365 day basis.
How is the interest estimated?
This calculator applies simple interest to a constant borrowed balance: balance multiplied by annual rate, divided by the selected day count, then multiplied by days. It does not model daily compounding or a changing debit balance.
Which day count basis should I use?
The 360 and 365 choices are calculation bases, not a claim about every broker's terms. They produce different daily estimates from the same annual rate. Check your statement or account terms for the basis that applies to your currency and account.
Is the monthly amount a bill estimate?
The monthly figure is a 30 day illustration calculated from the daily estimate. It is not a calendar month statement or a prediction of a broker bill.
What does the break even percentage mean?
The break even percentage is modeled interest for the selected period divided by the borrowed balance. It is the return on that borrowed amount needed to cover interest alone. It is not a return target on your full account equity and excludes price changes, fees, taxes, and other costs.
Related tools
Option Breakeven estimates an option expiration threshold. Margin Call Calculator estimates a separate maintenance scenario. This calculator estimates interest only.