https://bugs.documentfoundation.org/show_bug.cgi?id=173408
Bug ID: 173408
Summary: Incorrect and illogical example in the NPER function
help text
Product: LibreOffice
Version: 6.0.0.3 release
Hardware: All
OS: All
Status: UNCONFIRMED
Severity: normal
Priority: medium
Component: Documentation
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Description:
The help text for the NPER function in LibreOffice Calc contains an example
that is mathematically incorrect, logically inconsistent, and contradicts the
documented behavior of the function.
The current example states:
How many payment periods does a payment period cover with a periodic interest
rate of 6%, a periodic payment of 153.75 currency units and a present cash
value of 2,600 currency units.
=NPER(6%;153.75;2600) → Result: -12.02. The payment period covers 12.02
periods.
Problems in the example:
The function returns a negative value (-12.02). According to standard financial
mathematics and the function’s own documentation, a negative NPER result
indicates inconsistent or unrealistic parameters. It means that the payment
stream cannot reach the present value under the given conditions.
The help text incorrectly interprets the negative result as a positive number
of periods, stating that the payment period “covers 12.02 periods.” This
contradicts the actual output of the function.
The parameter combination used in the example is mathematically unsound:
PV is positive (cash inflow)
PMT is also positive (another inflow)
Rate is positive
With both PV and PMT being positive, there is no cash outflow, so the payment
cannot reduce or amortize the present value. This inevitably leads to a
negative NPER result.
This incorrect example appears to originate from the historical Excel/VBA
documentation. In that documentation, the same parameter set is used, and it
also produces a negative result. The example is presented without explaining
why the result is negative or what it means. LibreOffice seems to have adopted
this example without correcting the underlying issue.
Expected behavior:
The example should be corrected to use realistic financial parameters that
produce a positive number of periods, or
The help text should explicitly explain why the result is negative and what
such a negative value signifies.
Suggested corrected example:
A financially consistent example would use a positive PV (present value) and a
negative PMT (payment outflow):
How many periods are required to amortize a present value of 2,600 currency
units with a periodic payment of -153.75 and an interest rate of 6%?
=NPER(6%;-153.75;2600) → Result: 12.02 periods.
This reflects standard financial logic:
PV positive → amount owed or invested
PMT negative → payment made to reduce the amount
Actual Results:
Expected Results:
Reproducible: Always
User Profile Reset: No
Additional Info:
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