PDURATION in Excel: Periods to a Growth Target and Timing Units

=PDURATION(rate, pv, fv)

Rate is the rate per period, pv the present amount, and fv the desired future amount. All are required, and Microsoft requires all three to be positive. Unlike some cash-flow functions, this function does not ask for opposite signs on present and future amounts.

The independent model is LN(fv/pv)/LN(1+rate), derived from fv=pv×(1+rate)^n. The period’s length is determined by the rate convention supplied; the function has no date argument and does not convert years to months automatically.

=PDURATION(10%,1000,1331)

Expected result: 3 periods. The successive balances are 1100, 1210 and 1331. If the rate is annual, the answer is years; if it is monthly, the answer is months.

Do not insert -1000 as pv merely because a different financial function uses a cash-outflow convention. PDURATION explicitly requires a positive current value.

=PDURATION(5%,1000,1500)

Expected result: approximately 8.310386223 periods. This solves the compound-growth equation at a fractional exponent. It does not establish whether a real account pays interest continuously or only at discrete period boundaries.

If the question asks for the first completed whole period with balance at least 1500, use =ROUNDUP(PDURATION(5%,1000,1500),0), expected 9. That rounding is a stated reporting rule, not an additional feature of PDURATION.

At 5% per period, =1000*(1+5%)^8 gives 1477.455443789, below 1500. At nine periods the expected balance is 1551.328215979, above it.

The bracket explains why the whole-period threshold is nine while the algebraic answer is about 8.31. Keep both the exact model output and the rounded planning value if users need to understand the timing assumption.

Suppose 6% is an effective annual rate. An equivalent monthly rate is (1+6%)^(1/12)-1, rather than 6%/12. For a doubling target:

=PDURATION(6%,1000,2000)
=PDURATION((1+6%)^(1/12)-1,1000,2000)

Expected results are approximately 11.895661046 years and 142.747932551 months. The latter is twelve times the former, aside from floating-point rounding.

Using 6%/12 instead corresponds to a nominal annual quote compounded monthly, which has a different effective annual rate. Specify the quote’s convention before converting it.

If B2 contains the PDURATION result, =1000*(1+5%)^B2 should reproduce 1500 in the independent model. A tolerance-based comparison is appropriate; exact binary equality is not promised.

The function cannot incorporate regular contributions. A savings plan with additional deposits needs a cash-flow model rather than simply increasing pv or pretending all future deposits were present at time zero.

Microsoft documents #NUM! for invalid numeric arguments and #VALUE! for invalid data types, and explicitly requires positive rate, pv and fv. A zero rate is therefore outside the documented domain, even when a particular target might seem trivial.

For future growth planning, use fv≥pv. If both positive amounts are equal, the mathematical period count is zero. If fv<pv while rate is positive, the algebra gives a negative period count; that is not a future waiting time for a declining balance. These equal/lower-target controls are mathematical interpretations, not captured native boundary tests.

Native coercion, blanks and precision extremes remain unverified. Rates, fees and timing assumptions must be chosen independently; this tutorial does not predict a future return.

• Current documentation: the dedicated Microsoft reference lists Excel for Microsoft 365, Excel for Microsoft 365 for Mac, Excel 2024, Excel 2024 for Mac, Excel 2021, Excel 2021 for Mac, Excel 2019, Excel 2016.
• Introduced: Microsoft’s alphabetical catalog marks PDURATION as introduced in Excel 2013. Exact first build and platform-specific introduction dates remain unverified.
• Last functioning version: unknown; a current help listing is not a last-working-build test.
• Evidence checked: October 15, 2026. Official documentation was freshly retrieved; examples were independently calculated. No native Excel, Mac or web-client execution was performed.

• Microsoft PDURATION reference.
• Microsoft function catalog and introduction-marker explanation.
• Editorial testing standards.

Examples use English function names and comma separators. Expected numbers are rounded independent mathematical calculations; documented error expectations are labeled as such. They are not captured Excel output. All illustrative data and policies are fictional.