How to Use COUPDAYBS Function in Excel: Calculate Days Since Last Coupon

by Best Excel Tutorial Functions

Need to calculate how many days have elapsed since the last coupon payment on a bond in Excel? The COUPDAYBS function lets you find the number of days from the previous coupon date to the settlement date without manually counting calendar days. This guide shows you how, step-by-step.

1. Understand COUPDAYBS Function Logic

By default, COUPDAYBS returns the number of days from the previous coupon date to the settlement date based on the bond’s maturity and coupon frequency. So before you use COUPDAYBS, you must:

  • Have the bond’s settlement date and maturity date
  • Know the coupon frequency (annual, semi-annual, quarterly, or monthly)

2. Step-by-Step: Use COUPDAYBS to Calculate Days Since Last Coupon

✅ Step 1: Gather Your Bond Information

  1. Open your Excel spreadsheet
  2. In cell A1, enter the settlement date (for example: 3/15/2025)
  3. In cell A2, enter the maturity date (for example: 12/31/2027)
  4. In cell A3, enter the coupon frequency as a number (1=annual, 2=semi-annual, 4=quarterly, 12=monthly)
  5. Leave cell B1 empty for the COUPDAYBS result

✅ Step 2: Write the COUPDAYBS Formula

  1. Click on cell B1 where you want the result
  2. Type the formula: =COUPDAYBS(A1,A2,A3)
  3. Press Enter
  4. Excel returns the number of days since the previous coupon payment

Now the formula is complete. COUPDAYBS calculated exactly how many days have passed since the last coupon payment date.

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3. Tips for Better COUPDAYBS Calculations

  • Use cell references instead of hard-coded values so you can change dates without editing the formula
  • Make sure all dates are properly formatted as dates, not text, or the calculation will fail
  • Remember the coupon frequency codes: 1=annual, 2=semi-annual, 4=quarterly, 12=monthly

4. Bonus: Advanced COUPDAYBS with Accrued Interest Calculations

Want even more control? You can use COUPDAYBS with other coupon functions to calculate accrued interest or track coupon periods. Here’s an example:


Example 1: Days since last coupon for semi-annual bond
Settlement date: 3/15/2025
Maturity date: 12/31/2027
Frequency: 2 (semi-annual)
Formula: =COUPDAYBS(A1, A2, 2)
Result: 74 (days since 12/31/2024 coupon)

Example 2: Days since last coupon for quarterly bond
Settlement: 4/20/2025
Maturity: 6/30/2028
Frequency: 4 (quarterly)
Formula: =COUPDAYBS("4/20/2025", "6/30/2028", 4)
Result: 21 (days since 3/31/2025 quarterly coupon)

Example 3: Calculate accrual fraction of coupon period
Days since last coupon: =COUPDAYBS(Settlement, Maturity, Frequency)
Days in full period: =COUPDAYS(Settlement, Maturity, Frequency)
Accrual fraction: =Days since last / Days in period
Formulas:
Since last: =COUPDAYBS(A1, A2, A3)
Full period: =COUPDAYS(A1, A2, A3)
Fraction: =COUPDAYBS(A1, A2, A3) / COUPDAYS(A1, A2, A3)

Example 4: Calculate accrued interest to seller
Par value: 1000
Annual coupon rate: 5%
Frequency: 2 (semi-annual)
Days since coupon: =COUPDAYBS(Settlement, Maturity, Frequency)
Days in period: =COUPDAYS(Settlement, Maturity, Frequency)
Accrued: =(Par × Annual Rate / Frequency) × (Days since / Days in period)
Formula: =(1000 × 0.05 / 2) × (COUPDAYBS(A1,A2,2) / COUPDAYS(A1,A2,2))
Result: Accrued interest owed to previous bondholder

Example 5: Verify coupon period relationships
Days since last: =COUPDAYBS(Settlement, Maturity, Frequency)
Days to next: =COUPDAYSNCD(Settlement, Maturity, Frequency)
Total in period: =COUPDAYS(Settlement, Maturity, Frequency)
Verify: =COUPDAYBS(...) + COUPDAYSNCD(...) = COUPDAYS(...)
Formulas:
Since: =COUPDAYBS(A1, A2, A3)
To next: =COUPDAYSNCD(A1, A2, A3)
Total: =COUPDAYS(A1, A2, A3)
Check: =IF((COUPDAYBS(A1,A2,A3) + COUPDAYSNCD(A1,A2,A3)) = COUPDAYS(A1,A2,A3), "Correct", "Error")

Example 6: Determine percentage through coupon period
Percentage elapsed: =(COUPDAYBS / COUPDAYS) × 100
Formula: =(COUPDAYBS(A1,A2,A3) / COUPDAYS(A1,A2,A3)) × 100
Result: Shows how far into current coupon period (e.g., 40.8%)

This approach lets you calculate accrued interest, verify coupon timing, or track your position within the coupon period.

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Troubleshooting COUPDAYBS Functions

Sometimes users say that COUPDAYBS returns unexpected results or errors.

  1. Check if your dates are really formatted as dates, not text—dates as text will cause errors.
  2. Make sure the settlement date is before the maturity date.
  3. Verify that the coupon frequency is valid: 1, 2, 4, or 12 only.

Another common issue is that COUPDAYBS returns #NUM! error or an unexpected number.

  • Check that your settlement date is not after the bond’s maturity date.
  • Verify that your coupon frequency matches the actual bond (don’t use 2 for annual bonds, for example).
  • Make sure your maturity date is realistic and properly formatted as a valid date.

Learning how to use COUPDAYBS in Excel is a great way to calculate accrued interest and track coupon period timing accurately. You don’t have to manually count days since the last coupon—let COUPDAYBS calculate them and focus on your bond analysis.

Try it out and master bond coupon day calculations in Excel today!

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