Quick answer
Western usage means completed age. Where a record or tradition uses running age, the two differ by one and only a label prevents the confusion.
The same person, two numbers
Someone who has had 31 birthdays has a completed age of 31 and is living through their 32nd year. Both statements are true. "31" and "in their 32nd year" describe an identical situation and differ by one because they count different things — birthdays reached versus years begun.
Everyday English uses completed age almost exclusively, which is why "in his 32nd year" reads oddly and gets misread as meaning 32. Historical and formal writing uses running age more often, and legal records in some traditions do too.
Use this guide with the right tool: Open the Age Calculator for exact chronological age in completed years, calendar months and remaining days. If the question shifts, compare it with the Age at Last Birthday Calculator or the Age at Next Birthday Calculator.
Where it turns up
Older gravestones, parish registers, formal biographies and translated documents are the common sources. Latin records using "anno aetatis suae" typically mean the running year, so "anno aetatis suae 32" means a completed age of 31.
Some insurance and actuarial contexts use age at nearest birthday rather than last birthday, which is a third convention again: it rounds to whichever birthday is closer, so it can be one higher than completed age for anyone past the midpoint of their year.
Reconciling a one-year discrepancy
When two records disagree by exactly one year, the cause is one of three things: a running-age convention, a birthday that had not yet passed on one of the two reference dates, or a nearest-birthday rounding. All three produce the same visible symptom.
The diagnostic is to compare the reference dates and the month of birth. If the reference dates straddle the birthday, that explains it. If they do not, a convention difference is the likely cause, and the older or more formal source is the one more likely to be using running age.
Writing it unambiguously
In your own records, write completed age and say so if there is any chance of confusion. "31 (completed)" costs four characters and removes the question permanently.
When transcribing a historical record, keep the original wording alongside your interpretation rather than replacing it. "Aged 32 years [running age; completed age 31]" preserves the source and shows your reasoning, which is what a later reader needs.
Worked example
On 16 August 2026, someone born 18 November 1994 has completed 31 years, is in their 32nd year, and is 32 at nearest birthday, because that birthday is three months away. Check your own dates three ways and note which convention the form asks for.
Three numbers, three changeover dates
The worked example reads all three conventions on a single day. Following the same person — born 18 November 1994 — through one year of life shows that the three numbers do not change together. Two of them move on the birthday. The third moves months later, on a date nobody marks.
On Tuesday 17 November 2026, the day before the birthday, this person has a completed age of 31 years, 11 months and 30 days, is in their 32nd year, and is already 32 at nearest birthday, because the 32nd birthday is one day away. On Wednesday 18 November 2026 the completed age becomes 32 and the 33rd year begins, together, on the same morning. The running year and the completed age are locked to the same event, which is why they always differ by exactly one and never by anything else.
The nearest-birthday figure changes on its own schedule, halfway through the year. The span from the 32nd birthday to the 33rd is 365 days, so the midpoint falls 182 and a half days in. On Wednesday 19 May 2027 this person is 182 days past their 32nd birthday and 183 days short of their 33rd, so their age at nearest birthday is still 32 — by a single day. On Thursday 20 May 2027 the counts swap, 183 against 182, and the nearest-birthday age becomes 33, with no birthday anywhere near. By Wednesday 17 November 2027, the day before the next birthday, the three numbers read 32 completed, 33rd year in progress, 33 at nearest birthday.
The practical consequence is that two identical forms, asking for age at nearest birthday and answered either side of that May date, disagree by a year about the same person — with no birthday, and no change in the person, in between. A one-year discrepancy between two records does not even require two conventions: one convention, sampled on two dates, is enough.
The historical case from earlier in this guide can be worked the same way. A record of a death on 16 August 2026 described as "anno aetatis suae 32" means a completed age of 31, which puts the birth between 17 August 1994 and 16 August 1995 inclusive — a window of 365 possible birth dates. Read the same words as a completed age of 32 and the window shifts a full year earlier, to 17 August 1993 through 16 August 1994. The convention does not merely relabel the age; it moves the inferred birth year bodily, which is why the interpretation belongs in the transcription alongside the original wording.
The same three numbers also separate two people of identical completed age. On 1 June 2027 the person above has a completed age of 32 and a nearest-birthday age of 33, the May changeover having passed. Someone born on 20 January 1995, assessed on the same day, also has a completed age of 32 — but their nearest birthday is still the 32nd, 132 days behind them, rather than the 33rd, 233 days ahead, so their nearest-birthday age is 32. An actuarial table that groups by nearest birthday puts these two people in different age bands on the same day, while a table using completed age puts them in the same one. Neither table is wrong; they are answering the different questions this guide started with.
Common mistakes to avoid
- Reading 'in her 32nd year' as 32. It means a completed age of 31. The phrasing counts the year in progress.
- Averaging two records that differ by one. Identify which convention each used. An average matches neither source.
- Assuming insurance age means completed age. Some contexts use age at nearest birthday, which rounds up past the midpoint of the year.
Use the right calculator
Age Calculator gives exact age in years, months and days, Age at Last Birthday Calculator shows completed whole-year age, and Age at Next Birthday Calculator shows the next birthday and age reached.
Frequently asked questions
Which does this site use?
Completed age throughout, which is standard Western usage and what forms and legal thresholds mean.
What does 'anno aetatis suae' mean?
Literally 'in the year of his/her age' — a running-age formula, so the completed age is one less.
What is age at nearest birthday?
A convention used in some actuarial contexts that rounds to whichever birthday is closer, rather than counting only completed ones.