Months Between Dates

The difference is measured on the real calendar, respecting the length of each month it passes through. From January 1, 2026 to July 6, 2026 is 6 months and 5 days, which is 6 full months. That is not the same as dividing the days by 30, and the gap is not small. A month only completes when the day number repeats in a later month: January 15 to February 14 has not finished a month, and January 15 to February 15 has. Everything else here follows from that one rule. Order does not matter — the calculator sorts the two dates and returns a positive difference either way.

The same-day rule has one place where it genuinely breaks: months that do not contain the day you started on. What is one month after January 31? There is no February 31. This calculator resolves it by overflow. It requires the day number to be reached, so January 31 to February 28 comes back as 0 months and 28 days — the month has not completed — and the first full month arrives on March 3 in a common year, or March 2 in a leap year, when February has an extra day to give. Other systems resolve it by clipping instead, treating the last day of a short month as completing the month, so that January 31 to February 28 counts as a full month. Neither approach is wrong, but they disagree by a few days, and spreadsheet functions, banking systems and contracts do not all pick the same one. If a payment date or a notice period hangs on a month-end start date, read what the agreement says rather than trusting any calculator, this one included.

Treating a month as 30 days is convenient and wrong in a predictable direction. Only four months have 30 days; seven have 31, and February has 28 or 29. Run it over a year: 365 days divided by 30 gives 12.17 months. The five extra days are the accumulated 31sts. Over five years that is roughly a month of phantom time — enough to change how many payments a schedule contains. Some financial conventions embrace the approximation deliberately, using a 360-day year of twelve 30-day months so that interest periods are uniform and easy to compare. That is a modelling choice made with open eyes, not a description of the calendar. When you need the real answer — how long a warranty has actually run, how many months of tenure someone has — count the calendar. Dividing by 30.44, the average month length in the Gregorian calendar, is closer but still an average. It will never tell you whether the 15th has come round again.

The calculator gives you both parts: the count of complete months and the days beyond them. Which one you use depends entirely on what the leftover days are worth. When months are billing units — a subscription, a rent cycle, a loan instalment — the fraction usually does nothing. Eleven months and 29 days of a twelve-month plan is still eleven payments made, and the twelfth arrives on its date, not proportionally. When months measure eligibility, the fraction usually does not count either, and that is exactly where people get caught. A waiting period of six months is not satisfied at five months and 28 days. A benefit vesting at twelve months does not vest at eleven and a half. But when months measure something that accrues, the fraction is real money, and you need the day count to prorate it. That is why the result shows the calendar days too.

Of all the units on this page, only the second is a base unit of the International System; minutes, hours and days are accepted alongside it by convention. The month is not a unit of time at all in that sense — it is a calendar construct whose length depends on where in the year you are standing. That is why "three months" and "90 days" are different promises. Add 90 days to January 1 and you reach April 1 in a common year but March 31 in a leap year; three calendar months lands on April 1 in both. Across a longer term the wedge widens. So read the wording before you count. If the document says months, count months on the calendar. If it says days, count days. Converting between them to make the arithmetic easier is how a deadline moves without anyone deciding to move it.