Gregorian Calendar Calculator


Here you can learn how to compute the interval of time within one year. The example shows computing for the common year only, however, you can use the same way in the leap year case. Look for the table then. The black numbers indicate how many days passed since the last, interesting month (number 0 in the green field). The red numbers inform us how many days are left from our current month to month, which we are interested in (number 0 in the green field).


Let’s check the examples above marked “1” and “2”:
1. For instance now is 10 August. Seeing the numbers we can conclude, that the same day in February (10th) was exactly 181 days ago, and another 184 days left to the following 10th February. To check how many days ago 12 February occurred we need to subtract 2 days from the main output and will receive, that the period from 12th February to 10th August has exactly 179 days!
2. The second example is analogous to the first one. We have the 3rd of April. The last 3rd October was 182 days ago and the following 3rd October will occur after the next 183 days. Imagine, that we have some important event on October 21. Look on the field marked “2” where we can see, that between the same day in April and October is 183 days. Next, we need to add up 18 days (the period between the 3rd and 20th) to the 183 days mentioned before. From 3rd April to 21st October is exactly 201 days then!
A full one-year calculator is related to a 100-200-year calculator and a full 400-year cycle calculator is embedded on the bottom.


The paper shows the “time distances” since 1.01.1901 (top left). The dates were marked for every 50 years. Colors are related to the combinations, for which months and years are the same (see the days of the week finder )e.g. March 1951 and March 1973 are the same. The colors are not important. They inform us about the amount of weeks in the period. The number of full weeks is marked in bold and refers either to the common year or leap year.

The date 1.01.1901 is the traditional commencement of the calculation period. Hence I put the leap year for this date in case of starting the calculating period from e.g. 1904. Alternatively, You can do the calculation for the common year and next to add up a relevant amount of days from the one-year calculator (for the leap year) situated on the bottom.


We are able to count a certain period, which we are interested in in 3 ways:
1. “Random years range” – let’s imagine, that Mr Steven Fox was born on January 2, 1951. We would like to know how many “days” Mr. Steven at January 19, 2015, knowing that at this time he was 64.
See the field marked by number 2, which shows us exactly 64 years from the beginning of our calculator. Those 64 years include 23376 days, so from 2.01.1951 to 2.01.2015 passed 23376 days. Because we are interested in the January 19, 2015 date we have to add another 17 days to make a total outcome. Finally, we will know, that January 19, 2015, was exactly the 23393rd day of Steve Fox’s life. By the way look once again at the table no 2 and check, that 64-year-old Mr. Steven Fox has 3339,43 weeks. Taking into account, that January 2, 2015, was Friday the ’43 decimal notation indicates, that Mr. Steven was born on Tuesday.


2. “From the beginning” – If we want to know how many days passed from the beginning of the XXth century we need to look at field number 1. Then see, that from 1.01.1901 to end of the 1907 was exactly 2556 days. We are interested in the time period between 1.01.1901 to 23.06.1907. In this case, we need to refer to the one common year calculator on the bottom left (between 1901 and 1907 was one leap year only) and prior to the final calculation find December (the last green field with “0” situated on the bottom right). Now we can see, that between June and December is 183 days. In addition, our case refers to the end of 1907, December 31. To consider the 23rd of June we need to add up another 8 days to receive the right value of 191 days between 23.06 and 31.12. In our last step, we must subtract this value from 2556 days (the period between 1.01.1901 and 31.12.1907) to finally receive our amount of 2365 days. You can calculate this in a different way: first, calculate the period 1.01.1901 – 31.12.1906 (2191 days), and next add up 174 days (182 days from 1.01 to 1.07 minus another 8 days as a difference between 23.06 and 1.07), and then receive the same amount: 2365 days.

3. “The time interval difference” – Mr. John Cartney born on April 26, 1964, is going to retire on 1.09.2018. How many days will he have on this day? Let’s refer to field number 2 and field number 3. Field no 2 was discussed above. It contains 64 64-year periods since the commencement of the XXth century. Field no 3 informs us about 118 years since the commencement of the XXth century, that is end of the 2018. The first part of our calculation should be to calculate the time interval for the 1.01.1901-26.04.1964 period. We can do that in 2 ways Likewise in the examples above either add up the 1.01-26.04 period to another 63-year period or subtract the 27.04-31.12 period from 64 years. I would like to show you the calculation made in the first way. First I calculate the 1.01.1901-31.12.1963 period, which has 23010 days. Next, I need to add the 1.01-26.04 period (23010 days + 116 days) to receive an output of 23125 days. Remember, that 1964 was a leap year, so you need to refer to the one leap year calculator (bottom right). Alternatively, you can another 1 day to your 63-year period and make another calculation on the one common year calculator (bottom left).
Our next step needs to contain the calculation of the 1.01.1901 – 1.09.2018 period. See field number 3 then, from where you will read, that your interesting period counts 43099. The next step should state a calculation within one year only. Because of the 2nd part of the year (1.09), we can compute the days on a day calculator either for the common year or the leap year. We need to make a simple equation: 43099 – 121 = 42978 days (because 31.08 to 31.12 is 122 days, and between 31.08 and 1.09 is 1 day, which we need to subtract to receive finally 121).
Our last step is the difference between the shorter and longer periods. Thus we need to subtract the 1.01.1901 – 26.04.1964 period (23125 days) from the 1.01.1901 – 1.09.2018 period (42978 days). Finally, the equation should be: 42978 – 23125 = 19853 days!
This output is our answer: Mr John Cartney will have exactly 19853 days on September 1, 2018.


This calculator refers to the entire Gregorian Calendar 400-year cycle. The calculation looks the same as above. The 100-200 years calculator above was prepared due to the leap year 2000. This is a centurial year, which is exactly divisible by 400 and thanks to this you can use that calculator for up to 200 years. If you want to calculate the period of time for more than 400 years (e.g. 650 years) you must add 250 years (91311 days) to 400 years (total Gregorian Calendar cycle length – 146097 days) to receive 237408 days.
You can use this calculation to compute the duration of some astronomical phenomena or the duration of the motion of astronomical objects around the mother star.
Click to enlarge and see the full 400 years Gregorian Calendar calculator below: