Apple Numbers COUPDAYS: Length of the coupon period containing settlement
Calculate coupon-period length in Apple Numbers with COUPDAYS, distinguish full-period days from elapsed days and compare actual and 30/360 examples.
Verification status: See the evidence and test scope described in this guide. How formula examples are checked
Quick answer: Apple’s documented quarterly example returns 91 days for the coupon period containing April 2, 2010 settlement. COUPDAYS measures the whole period, not just the days already elapsed at settlement.
Syntax and defaults
=COUPDAYS(settle, maturity, frequency, days-basis)
Apple requires maturity after settlement. Frequency is 1, 2 or 4 payments per year. The optional days-basis defaults to 0; supported modes are 0 NASD 30/360, 1 actual/actual, 2 actual/360, 3 actual/365 and 4 European 30/360. Apple COUPDAYS help 15.4.
The period is the one containing settlement in the regular coupon schedule. It is not the entire span from settlement to maturity, and the result is not a coupon count. Keep the output as a number rather than applying a date format.
Reproduce the documented quarterly example
Enter these values in a fresh table:
| Cell | Input |
|---|---|
| B2 | =DATE(2010,4,2) |
| B3 | =DATE(2015,12,31) |
| B4 | 4 |
| B5 | 1 |
Enter =COUPDAYS(B2,B3,B4,B5) in B7. The documented reference is 91. The complete equivalent is:
=COUPDAYS(DATE(2010,4,2),DATE(2015,12,31),4,1)
Apple describes the period as April 1 through June 30, 2010. Counting those calendar days inclusively gives 30 + 31 + 30 = 91. Equivalently, subtract the boundary coupon date March 31 from June 30 to obtain 91 elapsed days. Subtracting April 1 from June 30 without inclusive counting would instead give 90; do not mix those endpoint conventions.
The published result is independently reproduced by calendar reasoning. It is not an observation from an authored Numbers workbook.
Compare full period with elapsed days
For the same dates, COUPDAYBS has Apple’s documented result 2, the days from March 31 to April 2. COUPDAYS is 91 because it includes the entire period containing that settlement.
The independently calculated remaining span is 89 days from April 2 to June 30. These three numbers play different roles: 2 elapsed, 91 full period and 89 remaining. They are consistent for this particular actual-day example, but the guide does not assert an unconditional identity across every day-count convention and boundary case.
A midmonth frequency comparison
Use settlement March 15, 2025 and maturity January 15, 2028 with basis 1. The independently enumerated regular schedules give:
| Frequency | Period boundaries around settlement | Actual period length |
|---|---|---|
| 1 | January 15, 2025 to January 15, 2026 | 365 |
| 2 | January 15, 2025 to July 15, 2025 | 181 |
| 4 | January 15, 2025 to April 15, 2025 | 90 |
For example, =COUPDAYS(DATE(2025,3,15),DATE(2028,1,15),2,1) has the independent reference 181. The semiannual period is not automatically 365/2: actual half-year intervals need not contain equal numbers of calendar days.
For basis 0 with the same semiannual midmonth dates, the independent 30/360 period is 180 day-count units. The explicit formula is =COUPDAYS(DATE(2025,3,15),DATE(2028,1,15),2,0). This ordinary midmonth comparison avoids unverified month-end adjustment details.
Practical use: audit a period fraction
In the actual/actual semiannual example, 59 days have elapsed since January 15 and the whole period is 181 days. The independent elapsed fraction is 59/181, about 0.3259668508. In the corresponding 30/360 example, the counts are 60 and 180, giving 1/3.
Those fractions differ for a reason. A worksheet that combines an actual elapsed numerator with a synthetic denominator may be using an intended mixed convention or may contain a mistake; make the selected basis and modelling purpose explicit instead of silently mixing the numbers.
A coupon-period denominator can help check accrued-interest or discount-timing calculations, but COUPDAYS itself returns no monetary amount. BONDDURATION uses cash-flow timing for a different financial measure. Do not treat period length as a price, payment entitlement or investment return.
Errors and scope limits
Check valid dates, maturity after settlement and the documented frequency/basis choices. Apple’s reference does not provide an exhaustive error-code table, so no exact error label is promised for an invalid frequency or equality boundary.
The examples establish basis 1 and ordinary basis 0 cases. They do not justify applying 365/frequency, 360/frequency or literal actual-day subtraction unconditionally to every mode. February endpoints, leap-year boundaries, settlement exactly on a coupon date and irregular first or last periods need separate evidence before generalization.
Availability and evidence scope
Apple Formulas and Functions Help 15.4 was checked October 18, 2026. Complete dates and independently calculated periods support the examples; no authored native execution or screenshot is claimed. The shared iWork reference does not establish first introduction, older-release support or parity across every client. This guide explains worksheet mechanics, not financial or contractual advice.