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Use the COUPDAYBS (coupon days before settlement) function to calculate the number of days from the beginning of the coupon period until its settlement date.

The number returned includes both the first day of the period and the settlement date.


COUPDAYBS(settlement, maturity, frequency[, basis])

The COUPDAYBS function has the following arguments:

Argument Data type Description
settlement (required) Date The bond settlement date — the date the bond is traded to the buyer.
maturity (required) Date The bond maturity date — the date when the bond expires.
frequency (required) Number

The number of coupon payments per year.


  • 1 for annual,
  • 2 for semi-annual, or
  • 4 for quarterly.
basis (optional) Number

The basis determines how many days exist in a year. 

A full year has:

  • 360 days when basis US 30/360, Actual/360, and EUR 30/360 are used;
  • 365 days when basis Actual/365 is used; and
  • 365 or 366 days when Actual/Actual is used.

US 30/360 is the default basis for COUPDAYBS. It can also be specified by entering 0.

To use a different type of day count basis, enter:

  • 1 for Actual/Actual,
  • 2 for Actual/360,
  • 3 for Actual/365, or
  • 4 for European 30/360.

Learn about the conventions used to calculate the day count for basis.




The COUPDAYBS function has the following constraints:

  • the settlement and maturity dates must be valid dates between 01/01/1900 and 12/31/2399;
  • the maturity date must be later than the settlement date;
  • the frequency must be either 1 (annual), 2 (semi-annual), or 4 (quarterly); and
  • the basis, when specified, must be either 0 (US (NASD) 30/360), 1 (Actual/Actual), 2 (Actual/360), 3 (Actual/365), or 4 (EUR 30/360).


The following tables show some example formulas using the COUPDAYBS function.

You can reference line items or list properties in your formula.

Formula Description Result
COUPDAYBS(DATE(2015, 1, 15), DATE(2018, 1, 31), 1, 1)

This example shows how the number of days before the settlement date can be calculated when a basis is specified.

The basis is given as 1 (Actual/Actual).

The example uses:

  • a settlement date of 01/15/2015,
  • a maturity date of 01/31/2018, and
  • a frequency of 1 (annual).
COUPDAYBS(DATE(2015, 1, 15), DATE(2018, 1, 31), 4)

In this example the number of days before the settlement date is calculated without specifying a basis. As a result, this defaults to US 30/360.


  • the settlement date is 01/15/2015,
  • the maturity date is 01/31/2018, and
  • the frequency is 1 (annual).

Excel equivalent