In the Start Date field, there’s a past date
In the Billing field, there’s a dropdown list with the values “Monthly”, “Quarterly”, “Semi-annually” and “Annually”
In the Next Billing field, I want a formula that calculates next billing date based on the values in the two previous fields. Next Billing should always be a upcoming date (or today).

Examples:

If Start Date is “2018-01-01” and Billing is “Monthly”, I want Next Billing to say “2021-09-01”
If Start Date is “2020-06-18” and Billing is “Semi-annually”, I want Next Billing to say “2021-12-18”
If Start Date is “2016-10-24” and Billing is “Annually”, I want Next Billing to say “2021-10-24”

I have tried to do this myself but I can’t work out how to do it. Can someone please help?

Hi Per. I’m not sure that I get your examples. In the “Monthly” case, you want to add 3 years and 9 months to the {Start Date}? In the “Semi-annually” case, you want to add 1 year and 6 months? I’m pretty sure that’s not what you mean, so I’ll answer the question that I think you’re asking. If I misunderstood, you can still use my answer, just change the SWITCH values to something else.

I just answered a question very similar to this one today. Put this formula in your {Next Billing} field.

It’s not that I want to add a specific amount of months in each example, I want the formula to calculate the next upcoming (future) billing date. Your formula gives me dates in the past. Next Billing should always be sometime in the future (or today).

Do you mean that you want to give the formula a {Start Date} that may be years in the past, set the {Billing} to “monthly” for example, and then have the {Next Billing} be the same day of month in the next month of this year? Just an example.

Yes, that’s exactly what I want. I just want to know “when is the next time I should send a bill to this customer based on it’s start date and billing interval?”.

Sometimes a formula has to be long in order to include all the logic.

One down side is that the longer the formula, the longer it takes Airtable to recalculate. On the other hand, Airtable will eventually complete the recalculations. While this formula is on the longer side, it is far from reaching the limits of Airtable’s capabilities, and it still recalculates reasonably quickly.

Another down side of long formulas is that they can be difficult to maintain, as there is no built-in way of including comments in a formula. This is why it is very important to have a quality formula to start with that covers all of your potential edge cases. If there is a small logic error in the formula that you don’t discover until after the formula is in production, it can be very difficult to root out the problem. This is also why I ask if you want to test any additional dates before purchasing the formula, while the algorithm is fresh in my mind. (I do write my formulas to make them easy to read, but even so it can be difficult to retrace the logic in these formulas after the fact due to the lack of comments.)

Mostly, I list the number of lines in the formula to indicate that I do not consider this to be a trivial formula that can be solved in only a few lines.

Thanks for clarifying! The only problem I can see in your test is the record with “Quarterly” as billing interval. Next Billing should be 2021-09-28, as I will bill this customer every quarter starting from March 28th. I.e March 28th, June 28th, September 28th and December 28th each year. Let me know if anything is unclear.

Thanks for the catch. This is what I mean about the importance of testing cases. I got mixed up between a quarter being 3 months versus 4 months. Lol. There are 4 quarters in a year, but each quarter should be only 3 months, not 4 months long.