Hi Alyssa,
I have one more question:
I'd like to calculate how long remained in the current year, and the formula is
=12-$[How_long_meet_deductible]-(13-$[Start_month])
However, I don't know how to make "month" shows in number format. For example: Jan=1; Feb=2; and so on.
I hope the question is clear, please let me know if you have any questions.
Thanks
Hi @Juice! 
To calculate time in months, you can use the MONTH() function. This would return the month of a given date.
For example, MONTH(TODAY()) would return "3", since we are currently in March. There are other similar time functions too, which you can find here: Honeycode Functions.
I'll note though, looking at your app it appears that your Start Month variable is a string ("January"). If that's the case, you can add another column to your Months table that has the corresponding number like this:
And your formula would then look something like: =12-$[How_long_meet_deductible]-(13-$[Start_month][MonthNumber])
Let us know if this helps, and if you have any other questions. 
