Quick answer
Add half the elapsed days to the earlier date. Odd spans land at midday, so decide whether to round down or up and say which.
The calculation
Count the elapsed days between the two dates, halve it, and add that to the earlier date. A 100-day span has its midpoint 50 days in. Nothing about month lengths or leap years enters, because the whole thing is done in days.
This is one of the few date operations with no convention attached to the main step. Working in days rather than trying to halve a years-months-days interval avoids the question entirely — halving '2 years 7 months' has no well-defined answer.
Use this guide with the right tool: Open the Date Midpoint Calculator for the exact midpoint date between two calendar dates. If the question shifts, compare it with the Days Between Dates Calculator or the Date Difference Calculator.
Odd spans and the half day
An odd number of elapsed days puts the true midpoint at midday. A 101-day span has its centre 50.5 days from the start. If you need a whole date, you round.
Rounding down gives the last date in the first half; rounding up gives the first date in the second. Either is fine and they differ by a day. For an anniversary or a milestone it rarely matters; for splitting a period into two halves that must not overlap, decide explicitly and apply it consistently to both halves.
What people actually use it for
Marking the halfway point of a relationship, a pregnancy, a project, a sentence, a deployment or a course. Splitting a reporting period. Finding a fair meeting point between two deadlines. Locating the centre of a historical span.
In each case the useful output includes the weekday, because a midpoint that lands on a Sunday is not much use for a planned event. It is also worth seeing the two halves as day counts, which makes an odd-span rounding decision visible rather than hidden.
More than two dates
The midpoint of several dates is a different question. The mean date — average the day numbers — is pulled by outliers. The median date, the middle one when sorted, is not. Which you want depends on whether you are describing a centre of mass or a typical value.
Neither is what a two-date midpoint calculator produces, so for a set of dates do the arithmetic deliberately rather than chaining pairwise midpoints, which gives a different and largely meaningless answer.
Worked example
None of this is difficult arithmetic. The part worth slowing down for is deciding which convention applies before you start.
Common mistakes to avoid
- Halving a years-months-days interval. There is no well-defined half of '7 months'. Convert to days, halve, then convert back.
- Ignoring the half day on odd spans. State whether you rounded down or up, particularly when splitting a period into non-overlapping halves.
- Chaining pairwise midpoints for several dates. That does not give the mean or the median. Calculate whichever you actually want directly.
Use the right calculator
The calculators below apply exactly the method described here, with the assumptions visible on the page.
Frequently asked questions
Does the midpoint account for leap years?
Yes, automatically — the calculation counts real elapsed days, so any leap day in the span is included.
Which way does this tool round?
It reports the midpoint date along with both half-lengths in days, so an odd span is visible rather than silently resolved.
Can I find the one-third or three-quarter point?
Yes, by the same method with a different fraction of the elapsed days. The rounding question applies in the same way.