Month Calculator

What the month calculator does

Some things are naturally counted in months rather than days. A billing cycle, a rental period, a baby's age, how long you have been in a job. This tool works that out. Give it two dates and it tells you how many whole months sit between them, the leftover days on top of those months, and as a bonus, how many days until the next monthly anniversary of your start date ticks over.

It is the right tool when "97 days" is a less useful answer than "3 months and a bit," which is how people actually think about rent, subscriptions, and milestones.

How to use it

1. Start Date. The earlier date.
2. End Date. The later date.

Press Calculate to see the months between, the exact months and days, and the days to the next monthly anniversary. Press Reset to clear them.

How the months are counted

It counts the whole months from the start date to the end date, the way you would tick them off on a calendar. The key rule, and the next section says more on this, is that a month only counts once the same day of the month comes around again. After the whole months are settled, it measures the leftover days that do not quite make another month, and reports both together as the exact time between.

An example with real numbers

Take 15 January to 20 April.

• January to April is 3 months, and since the 20th is past the 15th, all three are complete, so that is 3 whole months.
• Three months from 15 January is 15 April, and from there to 20 April is 5 leftover days.
• So the exact time between is 3 months and 5 days.
• The next monthly anniversary of the 15th after that is 15 May, which is 25 days away.

So you get 3 months, then 3 months and 5 days for the exact gap, and 25 days until the cycle rolls over to its next month.

When a month counts as complete

This is the part that decides whether you land on the right number, and it works just like a birthday does. A month is only finished when its date comes back around. So from the 15th of one month to the 14th of the month after is not a whole month yet, because the 15th has not arrived, it is 30-odd days but zero complete months. Wait one more day to the 15th and it clicks over to one month. The day of the month is the trigger, which is why the tool checks whether the end day has reached the start day before it counts the final month.

The days-until-next-month figure

Along with the count, the tool tells you how many days remain until the next monthly anniversary of your start date. If something started on the 15th, this is how many days until the next 15th rolls around past your end date. It is a genuinely handy number for anything that renews monthly on a fixed date, a subscription, a rent payment, a standing bill, because it tells you exactly how long until the next cycle begins rather than leaving you to count it off a calendar.

Questions people ask

How are the months counted?

As whole months by the day of the month. A month is counted only once its date comes back around, so the end day has to reach the start day for that month to be complete, just like a birthday.

What does the exact time between mean?

It is the whole months plus the leftover days that did not add up to another full month. So a gap might be 3 months and 5 days, which is more precise than rounding to either 3 or 4 months.

What is the days-until-next-month figure for?

It counts the days until the next monthly anniversary of your start date. It is useful for billing cycles and subscriptions that renew on the same date each month, since it tells you how long until the next one is due.

How is this different from a days between dates tool?

A days tool gives you the gap as a flat number of days. This one gives it in months and leftover days, which suits anything measured in monthly terms, like rent, tenancy, or a baby's age.