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# How to build formulas that automatically calculate interest and due dates
- URL: https://blog.jestor.com/interest-due-date-formulas-jestor/
- Published: 2026-07-10T14:55:49.000Z
- Updated: 2026-07-10T14:55:49.000Z
- Author: Bruno Bannach

In a payables table in **Jestor**, you can create a formula field that automatically calculates the value with late interest, and another that calculates the due date based on the issue date, with no need to manually update these values.

## Why does automating interest and due date calculations matter?

Calculating interest or setting a due date by hand, record by record, is the kind of repetitive task that eats up time and opens the door to human error, especially in finance tables with a high volume of entries.

## How to build interest and due date formulas in Jestor?

- Interest formula: using the original value field as a reference, the formula multiplies that value by a factor — for example, 1.10 to apply 10% interest.
- Due date formula: starting from an issue date field, the date-sum function adds a time interval to automatically calculate the due date.
- The interval can be configured in different units — days, months, etc.
- These same formula fields also support text concatenation and other combinations.

| Formula       | How to calculate                            |
| ------------- | ------------------------------------------- |
| Late interest | Original value × factor (e.g. 1.10 for 10%) |
| Due date      | Issue date + interval (days, months)        |

To build the interest and due date formulas:

1. In the table, add a formula-type column.
2. For interest, multiply the value field by the desired factor.
3. For the due date, use the date-sum function, selecting the issue date field, the numeric interval, and the time unit.

## Why choose Jestor to automate financial calculations?

Having this calculation automated directly in the finance table means the team doesn't need a parallel spreadsheet just to calculate interest or forecast due dates.

## Frequently asked questions

### Does the interest formula recalculate itself if the original value changes?

Yes, since it's a formula field, the result is automatically recalculated whenever the source value changes.

### Can I use a monthly interval instead of days?

Yes, the date-sum function accepts different units, including days and months.

### Do these formula fields work only for numbers and dates?

No, they also support text concatenation and other combinations within the same table.

### Do I need to rebuild the formula for every new record in the table?

No, the formula is created once in the field and applies automatically to all records.

## Reference video

Check out the [Jestor YouTube channel](https://www.youtube.com/@jestorbr?ref=blog.jestor.com) for more content like this.

## Discover Jestor

With Jestor, you can automate workflows, connect teams, and build internal systems your way — all without code and powered by AI. Discover Jestor at [jestor.com](https://www.jestor.com/?ref=blog.jestor.com) and see how to take your company's operations to a new level of efficiency and control.