Calendars: are the best example that humans (well, some) do love organization. Calendar is <insert-a-red-heart-here>. It is a physical record of the entire past, your list of planned events of the present and the time-map for future plans. We all owe one to the inventor of calendar, probably some intelligent exceptionally gifted roman horologist, for this algorithmic and systematic marvel !! The biggest problems of our generation: (i) Lack of time, and (ii) Lack of organization: Well Calendar has them both sorted for you.
There are many types of calendar. The Gregorian calendar is the calendar used in most of the world. It was introduced in October 1582 by Pope Gregory XIII as a modification of the Julian calendar implementing a system for adjusting the drift in the ‘tropical’ or ‘solar’ year that the inaccuracy had caused during the intervening centuries. It is a solar calendar. Bikram Samvat Calendar on the other hand is lunar calendar and in context of Nepal it also includes adjustment for solar tropical days. It is the official calendar of Nepal. It is a historical Hindu calendar used in the Indian subcontinent.
A question usually asked is: Is there any numerical relationship between Gregorian and Bikram Sambat Calendar? Well Not Exactly. But we have seen people adjust 57 years of difference of Gregorian Year and Bikram Sambat Year. What is that? That’s just an inaccurate but approximate relation, but it is limited to calendar years only. Doesn’t work similarly in the context of calendar months and calendar days. Many people also do adopt Knuckle Mnemonic for comparing different calendars upto calendar month, but its also not an accurate adjustment. No, it doesn’t work all the time, not at all for calendar days. The unhelpfulness of such methods has been parodied as “Thirty days hath September / But all the rest I can’t remember”.
So how does the Gregorian to Bikram Sambat Date Converter tools work? Well, they do not function from a mathematical relationship, but rather feed from a database of the historical records establishing relation between the calendars and also from the calendars already set for some time into the future. So, the alternative to a user is just to use a tool, nothing else.
Here is a link to the date converter tool that I made and the functions that it supports. Steps to Install:
Step 1: Download the Excel Addin File from this link. 
Step 2: Install the Addin File
(i) Open your “Microsoft Excel”
(ii) Go to “Files:
(ii) Go to “Options”
(iv) Go to “Add-ins” tab in the new window
(v) At the bottom at “Manage” Section choose “Excel Add-ins” and click “Go”
(vi) Click “Browse” and browse and select the file downloaded from Step 1
(vii) Click “OK” and return to Excel Spreadsheet
Step 3: You can start to use the tool
Functions available
1. AD_BS(insert_ad_date_here)
Output: BS Date
Note: The AD date should be recognizable by excel as date, else it will not work.
2. BS_AD(insert_bs_date_here)
Output: AD Date
Note: The BS date should be in the format YYYY.MM.DD, else it will not work. For BS dates where different delimiters like / or | are used, you can use the SUBSTITUTE tool to correct the delimiter and then use the tool
3. AD_BS_Long(insert_ad_date_here)
Output: BS Date in Long Form e.g. YYYY MMMM DD
Note: The AD date should be recognizable by excel as date, else it will not work.
4. NEPALI_DAY(insert_bs_date_here)
Output: Provides the Nepali Day of the BS Date
Note: Equivalent to DAY Function in Excel for Gregorian Calendar
5. NEPALI_MONTH(insert_bs_date_here)
Output: Provides the Nepali Month of the BS Date
Note: Equivalent to MONTH Function in Excel for Gregorian Calendar
6. NEPALI_YEAR(insert_bs_date_here)
Output: Provides the Nepali Year of the BS Date
Note: Equivalent to YEAR Function in Excel for Gregorian Calendar
7. NEPALI_DATE(NEPALI_YEAR, NEPALI_MONTH, NEPALI_DAY)
Output: Provides the compete Nepali Date based on the parameter
Note: Equivalent to DATE Function in Excel for Gregorian Calendar
8. NEPALI_DAYS_IN_A_MONTH(NEPALI_YEAR, NEPALI_MONTH)
Output: Number of calendar days in the particular Nepali Month
9. BEGINING_OF_NEPALI_MONTH(insert_bs_date_here)
Output: Returns the first day of the month of the particular date
Note: Equivalent to EOMONTH Function in Excel for Gregorian Calendar
10. END_OF_NEPALI_MONTH(insert_bs_date_here)
Output: Returns the last day of the month of the particular date
Note: Equivalent to EOMONTH Function in Excel for Gregorian Calendar
11. MONTHS_TOUCHED(bs_date_1, bs_date_2)
Output: Returns the number of months the two BS date touches
Note: Helpful for computing months for calculating fines for Income Tax Purposes
12. COMPLETE_MONTHS_TOUCHED(bs_date_1, bs_date_2)
Output: Returns the number of complete months the two BS date touches
Note: Helpful for computing months for contractual liabilities
13. MONTHLY_DATES(NEPALI_YEAR)
Output: Returns the array of the gregorian dates for the first day of the months of the particular Nepali Fiscal Year
Note: Helpful for preparing tax and other compliance calendars.
Please note this is an ARRAY function with SPILL feature.
Follow this post for more updates. You can later download more latest version of the converter tool here in the same post.