Apple Numbers COUPDAYBS: Days elapsed in the current coupon period
Use COUPDAYBS in Apple Numbers to count elapsed coupon-period days, with explicit dates, day-count bases and independently checked schedules.
Verification status: See the evidence and test scope described in this guide. How formula examples are checked
Quick answer: Apple’s example =COUPDAYBS(DATE(2010,4,2),DATE(2015,12,31),4,1) has a documented result of 2. The previous quarterly coupon is March 31, 2010; settlement on April 2 is two actual days later.
Syntax and required context
=COUPDAYBS(settle, maturity, frequency, days-basis)
Maturity must be after settlement. Frequency is 1, 2 or 4 coupon payments per year. Optional days-basis defaults to 0. The documented choices are 0 NASD 30/360, 1 actual/actual, 2 actual/360, 3 actual/365 and 4 European 30/360. Apple COUPDAYBS help 15.4.
The function asks how many day-count units have elapsed since the beginning of the coupon period containing settlement. It does not count days since issue, all days to maturity or the number of payments remaining.
Reproduce Apple’s complete example
In a fresh table enter:
| Cell | Input |
|---|---|
| B2 | =DATE(2010,4,2) |
| B3 | =DATE(2015,12,31) |
| B4 | 4 |
| B5 | 1 |
Enter =COUPDAYBS(B2,B3,B4,B5) in B7. Apple’s published reference is 2. The complete formula is:
=COUPDAYBS(DATE(2010,4,2),DATE(2015,12,31),4,1)
The quarter-end schedule has a prior coupon on March 31 and the next on June 30. March 31 to April 1 is one elapsed day, and April 1 to April 2 is another. This independently confirms the printed result without executing Numbers.
Keep the output in a plain numeric format. A result of 2 is a day count, not a calendar date serial to format as a date. The input cells, in contrast, should be recognizable dates.
A midmonth example with explicit schedule reasoning
Use settlement March 15, 2025, maturity January 15, 2028, semiannual frequency 2 and actual/actual basis 1:
=COUPDAYBS(DATE(2025,3,15),DATE(2028,1,15),2,1)
The regular maturity-anchored schedule uses January 15 and July 15 coupons. The prior date is January 15, 2025. Independent calendar subtraction gives 59 days to March 15: 31 days from January 15 to February 15, then 28 to March 15.
Adding six months to settlement would not identify the coupon schedule. The dates come from the regular maturity pattern, while settlement determines where inside a period the calculation occurs.
Compare a synthetic day basis
For the same midmonth inputs, change basis from 1 to 0:
=COUPDAYBS(DATE(2025,3,15),DATE(2028,1,15),2,0)
Under the ordinary 30/360 calculation, January 15 to March 15 is 60 day-count units, from (3-1)*30 + (15-15). The difference from 59 is expected: a synthetic day count is not necessarily an elapsed-calendar-day count.
These inputs avoid dates on the 31st and February endpoints. They do not establish all NASD or European month-end rules. Keep the selected convention visible when comparing worksheets rather than treating a one-day difference as automatically an error.
Practical use: inspect an accrued-interest fraction
For the actual/actual semiannual midmonth example, the complete January 15 to July 15 period contains 181 actual days. The independent elapsed fraction is 59/181, approximately 0.3259668508. COUPDAYS addresses that full-period denominator.
If an illustrative coupon amount is 30, applying this specific fraction gives about 9.779005525. This is a separate arithmetic model for the displayed period, not a universal guarantee of an instrument’s accrued-interest charge. Payment entitlement, settlement rules and irregular coupons may require different contractual treatment.
With the same March 15 settlement, annual, semiannual and quarterly schedules all happen to have January 15 as their prior coupon. Their elapsed actual day count is therefore 59 in each case, but their next dates and full-period lengths differ. Equal COUPDAYBS outputs do not imply equal coupon schedules.
Avoid confusing related functions
ACCRINT totals interest since issue under Apple’s documented contract, even after the first coupon. COUPDAYBS supplies an elapsed period count instead. COUPDAYS supplies the complete coupon-period length. Those purposes are distinct; copying one function name into another formula can silently change the question being answered.
The official constraints do not supply an exhaustive error-code table. Check maturity after settlement, supported frequencies, valid basis choices and real date values. Settlement exactly on a coupon boundary, irregular periods and date-text coercion are outside these verified examples; do not infer their exact results or errors.
Availability and evidence scope
Checked October 18, 2026 against Apple Formulas and Functions Help 15.4. The published example and independent calendar calculations are separate from runtime evidence: no native Numbers workbook or screenshot was produced. Introduction release, older-version coverage and client-by-client parity are not established by the shared help. This is spreadsheet mechanics rather than trading or legal guidance.