# Margin Interest Calculator

URL: https://speedycalculator.com/calculators/finance/margin-interest/
Last updated: 2026-10-25

> The margin interest calculator works out how much interest a broker charges on money borrowed in a margin account, for any number of days, using the 360-day year most brokers apply.

## Inputs

- Amount borrowed
- Annual margin interest rate (%)
- Number of days
- Day count

## Results

- Margin interest
- Interest per day
- Interest for a full year

## Formula

```
Margin interest = amount borrowed × annual rate × days ÷ 360
Daily interest = amount borrowed × rate ÷ 360
```

## Explanation

Buying on margin lets you invest borrowed money, but you pay interest every day the loan is outstanding. Rates often run 8–13% at major brokers for smaller balances, so margin only pays if your investments beat that rate after tax.

### How to use the Margin Interest Calculator

- **Amount borrowed**
- **Annual margin interest rate**
- **Number of days**
- **Day count**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the amount borrowed, the annual margin rate and the number of days, and choose the day-count convention.

### Tips

- Use the nominal annual rate and pick the compounding frequency your bank or broker states.
- Small differences in return or fees compound into large differences over decades.
- Run the calculation with a cautious, a central and an optimistic return to see the range of outcomes.
- Past returns do not guarantee future returns – nothing here is investment advice.

### Common mistakes to avoid

- Comparing an APR with an APY or effective rate.
- Ignoring inflation, taxes and fees when judging a real return.
- Entering a percentage as a decimal (5 instead of 0.05 is correct here).

### Inputs explained

FieldWhat to enterAmount borrowedAmount in your currencyAnnual margin interest rateIn %Number of daysA numberDay countChoose one: 360-day year (most brokers), 365-day year

### What each result means

- **Margin interest** = [Amount borrowed]×[Annual margin interest rate]÷100×[Number of days]÷[Day count]
- **Interest per day** = [Amount borrowed]×[Annual margin interest rate]÷100÷[Day count]
- **Interest for a full year** = [Amount borrowed]×[Annual margin interest rate]÷100×365÷[Day count]

### Example values

How the main result changes when **Amount borrowed** changes and everything else stays at the example values above:

Amount borrowedMargin interest12,500114.5818,750171.8825,000229.1731,250286.4637,500343.7550,000458.33

## Worked example

Inputs — Amount borrowed: $25,000; Annual margin interest rate: 11 %; Number of days: 30; Day count: 360-day year (most brokers).

Results — **Margin interest = $229.17**; Interest per day = $7.64; Interest for a full year = $2,788.19.

## FAQ

**How is margin interest calculated?**
Daily on the borrowed balance, usually using a 360-day year, and charged monthly.

**Is margin interest tax-deductible?**
In the U.S., as investment interest expense up to your net investment income, if you itemize.

**What are typical margin rates?**
Often 8–13% at large brokers for small balances; lower for large balances.

**What formula does the Margin Interest Calculator use?**
Margin interest = amount borrowed × annual rate × days ÷ 360.


## Sources

- [FINRA – Margin accounts](https://www.finra.org/investors/learn-to-invest/advanced-investing/margin-accounts)