Margin Interest Calculator

Estimate daily, monthly, annual, and holding-period margin interest from a debit balance, annual margin rate, cash offset, and broker day-count basis.

Margin carry-cost planner Estimate the financing drag on a margin debit balance from the quoted annual margin rate, the broker day-count convention, the planned holding period, and any cash balance that reduces the interest-bearing amount.

Day-count basis

Many brokers accrue margin interest daily using a 360-day basis, but some account agreements use 365.

Display currency

Switch the money display without changing the financing assumptions.

Result

$150.31

Estimated margin interest over 45 days on an interest-bearing balance of $13,000.00 at 9.25% annual rate using a 360-day basis.

Daily interest
$3.34
30-day estimate
$100.21
Annual estimate
$1,202.50
Break-even gain
1%
Cash offset reduces carry cost Keeping $2,000.00 in the account reduces estimated interest by $23.12 over the entered holding period.

Loan balance

$15,000.00

Gross broker debit balance.

Interest-bearing balance

$13,000.00

Net balance used for interest accrual.

Total due at end

$15,150.31

Loan balance plus estimated holding-period interest.

Planning note

The implied daily rate is 0.03%. This planner assumes a constant quoted margin rate and a flat debit balance for the whole period, so it excludes broker tier changes, compounding of unpaid interest, and balance changes from trading activity.

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Financing Cost

Margin interest calculator guide: daily accrual, holding-period cost, and cash offset savings

A margin interest calculator estimates how much it costs to carry a margin loan over time. That financing drag matters because margin investing is not just a leveraged market bet. It is also a borrowing decision. Even if the position value holds steady, interest can still reduce or erase the economic benefit of staying in the trade, especially when rates are high or the balance is carried for many days or weeks.

How margin interest is generally accrued

Brokerage firms typically quote an annualized margin rate, but the charge is often accrued daily against the account’s adjusted debit balance. That means the economic cost of borrowing depends on four practical inputs: the debit balance, the annual margin rate, the number of days the balance is outstanding, and the broker’s day-count convention, often 360 days and sometimes 365.

This calculator converts that annualized rate into a daily carry cost and scales it over a chosen holding period. It also lets you apply a cash offset. That matters because some account structures reduce the interest-bearing balance when cash or sweep balances are present, lowering the effective financing burden even though the gross loan balance itself is still visible in the account.

Why the holding period matters as much as the quoted rate

A margin rate can look manageable on an annual basis but still create a meaningful drag when a leveraged position is held through a volatile or low-return period. A trader who expects a quick move may tolerate the carry cost, while a longer-term holder needs a larger asset gain just to break even against the financing expense.

That is why the calculator shows daily, 30-day, annualized, and custom holding-period interest side by side. The annual rate is the headline number, but the real planning question is how much interest accumulates over the days you expect to keep the loan outstanding.

Daily rate = Annual margin rate / Day-count basis

Converts the quoted annual rate into the daily accrual rate used to estimate financing cost.

Holding-period interest = Interest-bearing balance × Daily rate × Days outstanding

Estimates the financing cost when the debit balance is assumed to remain flat over the chosen period.

Break-even gain = Holding-period interest / Gross loan balance

Shows the percentage gain needed on the financed capital just to offset the entered interest cost.

Why cash offsets can reduce margin cost

Some brokerage agreements calculate interest on an adjusted or net debit balance rather than on the gross loan alone. If part of the account is held in cash or sweep balances, that cash can reduce the amount on which interest is charged. The gross debit still exists, but the interest-bearing balance can be lower than the headline borrowed amount.

This distinction is useful because investors sometimes focus only on the gross debit balance and miss how much the financing cost changes when idle cash is left in the account. The opposite is also true: if cash is withdrawn or redeployed, the interest-bearing balance can rise even when the securities position itself does not change.

What this margin-interest planner does not cover

This calculator assumes a constant quoted margin rate and a flat debit balance for the whole holding period. It does not model broker tier changes, compounding of unpaid interest, trading activity that changes the balance, special margin rates for hard-to-borrow names, or account-level house rules. It is a carry-cost planner only.

Use the result to understand financing drag, not as a complete statement of what your broker will charge. The exact daily accrual method and the way cash balances offset margin debit can vary by firm and by account agreement.

Further reading

Frequently asked questions

Why does the calculator ask for a 360-day or 365-day basis?

Because brokers do not all use the same day-count convention when turning an annual margin rate into a daily accrual. A 360-day basis produces a slightly higher daily interest amount than a 365-day basis at the same quoted annual rate.

 Why can margin interest matter even if the stock price does not fall?

Because interest is a financing cost, not a market move. A flat or only slightly rising position can still underperform once the carrying cost of the margin loan is included.

 Does a cash balance always reduce margin interest?

Not always in the same way. Many firms use an adjusted debit balance or similar netting concept, but the exact treatment depends on the brokerage agreement and account setup.

 Does this calculator include changing rates or unpaid-interest compounding?

No. It assumes one quoted annual rate and one flat balance for the whole entered period, so it is best used as a planning estimate rather than an exact broker statement.

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