You will often want to work out the interval between two dates when working on a chronology. Chronolator provides a tool to do this for you when you press Tools > Age Calculator on the Chronolator toolbar.
If you have not used the Age and Interval Calculator before in this document, Date 1 has today's date in it, and Date 2 is blank. If you have used it before and saved the document, the last two dates you used will be shown.
You can type dates into the boxes in many formats. As you type, Chronolator displays what it thinks you mean next to the box. When Chronolator can interpret dates in both boxes, it calculates the interval between them. The interval is shown as a number of days and as a number of years, months and days. It does not matter which date is the earlier one.

You can copy the interval information to the Clipboard by pressing the Copy button, and then paste it into your document. The example above is copied to the Clipboard as 1 year, 11 months, 27 days (514 days). Once pasted into the document, you can edit it as you choose.

Using the Age and Interval Calculator is quite straightforward, but it is worth noting some details about how it works under certain circumstances. (If you are not interested in the minutiae of Date calculations, stop reading now and just use the calculator!).

Awkward calendars

'Thirty days have September, April, June and November' . . .  We are taught this rhyme when we are young, and learn to cope with the different number of days in each month over many years. However, innocent as it sounds it provides many a stumbling block when working out the interval between two days. The numbers of days between two dates is always unequivocal, but if we want to give this as 'x Years, y Months, z Days' we come across problems of interpretation. The following sections give examples of these problems and describe how Chronolator deals with them. There is no single 'right method'; we hope that Chronolator's results match most people's interpretations.

Easy calculations

When the Day number of the later date is equal to or larger than that of the early date, things are quite straightforward:

Slightly harder calculations

When the Day number of the later date is less than that of the early date, things can get a bit harder. However, as long as the Day number of the early date is less than or equal to the number of days in the month before the later date, there is not too much of a problem:

Most people would probably work this out as follows:

1. One year from 31 January 2001 = 31 January 2002
2. Adding 4 months takes us to 31 May 2002
3. Adding 1 final day gets to our target, 01 June 2002
4. That is, 1 year, 4 months, 1 day in all

So far, so good!

Difficult calculations

Now look at what happens when the Day number of the early date is more than the number of days in the month before the later date:

Comparing this to the previous example, 01 May 2002 is exactly one month earlier than 01 June 2002, so we might expect the answer to be exactly one month less; that is, 1 year, 3 months, 1 day.

However, if we use the same method as above:

1. One year from 31 January 2001 = 31 January 2002
2. Adding 3 months takes us to 31 April 2002!
3. But April only has 30 days, so we must already have arrived at 01 May 2002

That being the case, our interval is 1 year, 3 months, 0 days in all - one day less than expected!

The Chronolator solution

The Age and Interval Calculator works so that the above 'surprise' does not occur. From a date at the end of a month to the first of another month is always x Years, y months, and 1 day. For example:

This solution looks very plausible, but it does give rise to an anomaly. For example, the interval from 30 January to 01 May is the same as that from 31 January!

On balance, we feel that this solution most likely does accord with what most people want. However, if you disagree, please let us know by making a suggestion at www.chronolator.com/suggest-form.htm.