LOGN computes the logarithm of a positive value to a base you supply: =LOGN(81;3) has the mathematically expected result 4, because 3⁴ = 81. This is the Calligra-documented two-argument alternative to LOG/LOG10 (base ten) and LOG2 (base two).

=LOGN(value;base)

• value (required, first): numeric input or reference whose logarithm is required; it must be greater than zero for a finite real logarithm.
• base (required, second): numeric logarithm base. For a finite, real-valued logarithm, base > 0 and base ≠ 1. A base between 0 and 1 is mathematically valid and reverses the usual direction of the logarithm.
• Defaults: neither argument is optional in the KDE handbook’s LOGn(value;base) signature; do not assume an omitted base defaults to ten.
• Return: floating-point exponent satisfying base ^ result = value. Argument order matters: the first is the value, the second is the base.
• Naming: The handbook styles this name LOGn, but the 26.08.2 registry registers the primary function LOGN in uppercase. It is not an alias of LOG in the canonical primary-name inventory, although both use the same implementation symbol in source.

This guide is release-scoped to Calligra Sheets 26.08.2 (KDE’s release listing dated 2026-10-08). The function is present both in the official stable-KF6 function handbook and in KDE’s pinned 26.08.2 source-function registry; references were accessed 2026-10-11. The handbook’s surrounding revision may be older than the release: source registration documents that a name is available in that release’s code, not that it was executed or enabled in a particular Linux package or other platform. Calligra recommends Linux packages/Flatpak; installed versions and optional components can differ.

In a cell, start a formula with =. The KDE English documentation uses semicolon (;) as the multiple-argument separator; the examples use periods for decimal points. Actual entry conventions may vary with locale or build. Use the installed function selector to confirm locally and keep input columns numeric, not numeric-looking text. Results are floating-point values; displayed precision is controlled by cell formatting. All results below are expected mathematical values, not observed Calligra 26.08.2 outputs.

1. Label A1 Positive value, B1 Valid base and C1 Logarithm.
2. Enter the A and B inputs from the table, with numeric cells rather than quoted text.
3. Enter =LOGN(A2;B2) in C2 and fill it down to C6. Both inputs are required.
4. Check the result by asking whether B2^C2 equals approximately A2.

Check the KDE examples independently: LOGN(12;10) is approximately 1.07918125, while LOGN(12;2) is about 3.58496250. The difference is solely the selected base.

Suppose an amount grows by a constant fractional rate r per period, and you want to know when it will reach a target. The idealized model is target = start × (1+r)^t. Solving for t gives t = LOGN(target/start;1+r) when the start and target are positive and the growth factor is positive and not one.

• Enter D2 = 100 (start), E2 = 200 (target), F2 = 0.10 (rate per period, meaning 10%).
• In G2 enter =LOGN(E2/D2;1+F2). The expected fractional number of periods is approximately 7.2725409.
• For whole periods until the target is met or exceeded under uninterrupted 10% compounding, enter =ROUNDUP(LOGN(E2/D2;1+F2);0); expected 8 periods.
• If you want to guard the domain for the growth case, use =IF(AND(D2>0;E2>0;F2>0);LOGN(E2/D2;1+F2);"Check inputs"). This guard is specific to positive growth; a general logarithm base may legally be between zero and one. The formula is proposed and not Calligra-executed.

The model assumes constant compounding per period, no fees, no taxes and no interruptions. A stated 10% must be entered as 0.10 or a percent-formatted 10%, not 10 (which would be 1000%).

• base = 1: the logarithm is mathematically undefined even when the value is 1; do not assume LOGN(1;1) returns zero.
• base ≤ 0 or value ≤ 0: outside the real-logarithm domain. KDE’s handbook specifies float argument types but does not provide a complete set of native error-token examples. No exact error code is claimed here.
• 0 < base < 1: mathematically allowed: for example, LOGN(4;0.5) = −2, because 0.5⁻² = 4. A negative result does not imply a failed formula.
• Wrong argument order: LOGN(2;8) is 1/3, not 3. The desired LOGN(8;2) produces 3.
• Missing base: Calligra’s LOGN(value;base) requires both values; unlike Excel’s LOG(number,[base]), this documented form has no omitted-base default.
• Rounded display / threshold decisions: when applying ROUNDUP to an approximate log close to a whole number, small floating-point errors may matter. Check boundaries in an installed Calligra build.
• Locale and input parsing: the official English handbook shows semicolon separators. If a pasted formula fails, check the installed locale and whether the inputs were read as numbers.

Excel documents LOG(number,[base]), and LibreOffice Calc documents LOG(Number [; Base]): in those programs the base is optional and defaults to 10. The closest documented Calligra equivalent for a specified base is LOGN(value;base), not LOG(value;base). For a fixed base in Calligra, use LOG2(x) or LOG10(x). Translate both the function name and argument separators when moving formulas between applications; do not infer cross-program compatibility solely because numerical examples match. No migration test was executed.

• Calligra Sheets — function documentation
• official stable-KF6 function handbook
• KDE Calligra 26.08.2 source registration
• LibreOffice Calc mathematical functions

Verification status: Official documentation checked; example outcomes were independently reasoned or arithmetically checked where applicable. Not executed in Calligra Sheets.

• No genuine Calligra Sheets screenshots are included; this guide does not use mock application images.