# Understanding Day-Count Conventions: Types and Uses in Finance

![Day-Count Convention: A standardized methodology for calculating the number of days between two dates.](https://www.investopedia.com/thmb/v6DCyykfB-ZsXY2nclo0BvhogAo=/1500x0/filters:no_upscale():max_bytes(150000):strip_icc()/daycount.asp-FINAL-2-dc324a4924d04cdc997d97e402695a30.png)

*— Investopedia / Joules Garcia*

## What Are Day-Count Conventions?

Day-count conventions, including common types like 30/360 and actual/365, are essential in calculating accrued interest on financial instruments such as bonds and [swaps](https://www.investopedia.com/articles/optioninvestor/07/swaps.asp). These methods standardize the process of determining the number of days between two dates, thus affecting interest calculations and present values. Understanding these conventions is crucial for investors and financial professionals navigating complex financial markets.

### Key Takeaways

*   Day-count conventions are crucial in calculating accrued interest or present value for bonds, swaps, and other financial instruments.  
    
*   Common day-count conventions include 30/360, 30/365, actual/360, actual/365, and actual/actual, each used depending on the financial instrument and market.  
    
*   The actual/360 method is often used for money market deposits, while the actual/actual basis is typical for U.S. Treasury securities.  
    
*   Interest rate swaps commonly utilize a 30/360 or 30/365 day-count for fixed-rate legs and variations of actual/360 or actual/365 for floating-rate calculations.  
    
*   The LIBOR is a benchmark rate typically based on the actual/360 day-count, except for the British pound, which uses actual/365.

## Deep Dive Into Day-Count Conventions

The day-count conventions apply to swaps, mortgages, and forward rate agreements as well as bonds. Many of the rules and definitions for applying the day-count convention are set forth by the International Swap Dealers Association, which provides documentation for a wide range of financial transactions.

For example, an agreed-upon day-count convention would be used to calculate the amount of [accrued interest](https://www.investopedia.com/terms/a/accruedinterest.asp) or the [present value](https://www.investopedia.com/terms/p/presentvalue.asp) (PV) when the next coupon payment is less than a full coupon period away.

## Common Types of Day-Count Conventions

Among the most common conventions are 30/360, 30/365, actual/360, actual/365, and actual/actual.

*   30/360: calculates the daily interest using a 360-day year and then multiplies that by 30 (standardized month).
*   30/365: calculates the daily interest using a 365-day year and then multiplies that by 30 (standardized month).
*   actual/360: calculates the daily interest using a 360-day year and then multiplies that by the actual number of days in each time period.
*   actual/365: calculates the daily interest using a 365-day year and then multiplies that by the actual number of days in each time period.
*   actual/actual: calculates the daily interest using the actual number of days in the year and then multiplies that by the actual number of days in each time period.

## Day-Count Conventions in Financial Instruments

Each [bond market](https://www.investopedia.com/terms/b/bondmarket.asp) and financial instrument has its own day-count convention, which varies depending on the type of instrument, whether the interest rate is fixed or floating, and the country of issuance. [Bonds](https://www.investopedia.com/terms/b/bond.asp) and notes issued by the U.S. Treasury earn interest calculated on an actual/actual basis. This means all days in a period carry equal value; it also means the length of coupon periods and the resultant payments vary.

The interest on most money market deposits and [floating-rate notes](https://www.investopedia.com/terms/f/frn.asp) is calculated on an actual/360-day basis. The major exception is those denominated in the [British pound](https://www.investopedia.com/articles/forex/11/five-reports-affect-the-pound.asp), for which interest is calculated on the actual/365 basis. Currencies that are, or have been, closely related to the British pound, such as the Australian, New Zealand, and Hong Kong dollars, also use 365 days.

The fixed-rate leg of an [interest rate swap](https://www.investopedia.com/terms/i/interestrateswap.asp) and most fixed-rate bonds use either the 30/360 or 30/365 convention. This means every month has 30 days, and every year is treated as having either 360 or 365 days. [Swap markets](https://www.investopedia.com/articles/trading/11/introduction-swap-market.asp) using the 30/360 convention for the fixed rate of a swap include the [U.S. dollar](https://www.investopedia.com/terms/forex/u/usd-united-states-dollar.asp), the [euro](https://www.investopedia.com/terms/e/euro.asp), and the [Swiss franc](https://www.investopedia.com/terms/c/chf.asp). Swaps in British pounds and [Japanese yen](https://www.investopedia.com/terms/forex/j/jpy-japanese-yen.asp) typically use the 30/365 convention. Australia, New Zealand, and Hong Kong also follow the UK standard.

The floating-rate leg of most interest rate swaps uses an actual day count with a 360 or 365-day year. Markets with a 30/360 fixed-rate leg, like U.S. Dollar markets, use actual/360 for the floating-rate leg. Those that use 30/365 on the fixed-rate leg use actual/365 on the floating-rate leg.

The [London InterBank Offered Rate](https://www.investopedia.com/terms/l/libor.asp) (LIBOR) is the most commonly used benchmark interest rate and is posted daily at 11:45 a.m. London time.

> **Important**
>
> The Intercontinental Exchange, the authority responsible for LIBOR, will stop publishing one-week and two-month USD LIBOR after Dec. 31, 2021. All other LIBOR will be discontinued after June 30, 2023.

Most currencies calculate LIBOR interest using an actual/360-day basis; the British pound is a major exception, using the actual/365-day basis.

## The Bottom Line

A day-count convention standardizes the calculation of days between dates for financial instruments like bonds and swaps, helping determine accrued interest and present value. Common methods include 30/360, actual/360, actual/365, and actual/actual, each suited to different instruments and markets.

Understanding these conventions is crucial for financial professionals managing investments, calculating interests, and navigating various financial agreements.  

> **Article Sources**
>
> 1.  Intercontinental Exchange. "[LIBOR](https://www.theice.com/iba/libor)."