Adding calculated fields

When to use calculated fields

A calculated field is a Number or Currency field whose value is worked out automatically from other fields on the same form. The user doesn't fill it in — they just see the result update as they fill in the inputs.

Use them whenever the form contains numbers that follow on from each other:

• Total cost worked out from a quantity multiplied by a unit price
• Net amount from gross minus VAT
• Sum of line items in a snag list, daywork sheet or materials list
• Average condition score across several inspection ratings
• Headcount totals when several teams report their numbers separately

The point is to remove the chance of arithmetic mistakes — the form does the maths the moment all the inputs are in.

The eight operations

When you turn a field into a calculated field, you pick from eight operations:

The first four work on a fixed set of input fields. The last four work across all the rows in a Repeating section — handy for totalling line items.

How to set up a calculated field

1. 1

   Drag a Number or Currency field onto the canvas — the only field types that can be turned into calculations.

2. 2

   Click the field to select it, then open its settings on the right.

3. 3

   Scroll to the Calculated section and tick Make this a calculated field.

4. 4

   Pick the operation from the dropdown.

5. 5

   Pick the field (or fields) the calculation should use. For Add, Subtract, Multiply and Divide, pick the specific input fields. For Sum, Smallest, Largest and Average, pick the field inside a repeating section that you want to total up.

6. 6

   Save and preview the form. The calculated field is now display-only — its value updates live as users fill in the inputs.

Hidden fields don't count

Calculated fields only use fields the user can actually see as inputs. If one of the fields feeding the calculation is hidden by a show/hide condition, it's left out of the maths, even if it had a value entered earlier.

This is intentional — it lets you build forms where the result reflects what was actually filled in, rather than stale data hidden in the background.

For example, a "Total cost" field that adds up "Materials cost" and "Labour cost" will:

• Add both when both are visible
• Add only "Materials cost" if "Labour cost" is hidden by a condition
• Show 0 if both are hidden

Live updates as the user types

Calculated fields update on every change. As the user types, picks an option or adds a row to a repeating section, the calculation runs again and the result updates straight away. It feels instant, which is part of what makes calculated fields nice to use on long forms.

Currency vs plain Number

If the calculated field is a Currency field, the result is shown formatted with the £ symbol and the right number of decimal places. If it's a plain Number field, the result is shown as a regular number with the decimal places you've set in the field's options.

Totalling line items in a repeating section

Sum, Smallest, Largest and Average really come into their own with a Repeating section. The classic pattern is a list of line items with a grand total at the bottom:

1. 1

   Add a Repeating section.

2. 2

   Inside the section, add a Number field for Quantity and a Currency field for Unit price.

3. 3

   Inside the same section, add another Currency field called Line total and set it as a calculated field that Multiplies Quantity by Unit price.

4. 4

   Outside the section, add a final Currency field called Grand total and set it as a calculated field that uses Sum on the Line total field.

The Grand total now updates live as the user adds more line items — exactly what you want for a daywork sheet, a quotation, or a materials list.

Real-world examples

• Daywork sheet — line items with quantity and rate, a calculated line total per item, and a sum-based grand total at the bottom
• Inspection scoring — multiple condition ratings as Number fields, and a calculated average to give an overall score
• Concrete pour — bag count and bag weight as inputs, and a calculated total weight
• Snag count — a sum-based calculated field that counts the rows in a snag-list repeater

A few things to watch out for

• Calculated fields can't reference other calculated fields in a chain. If you need a chain of maths, do all the steps inline rather than splitting them across multiple calculated fields
• Show/hide conditions can't read calculated values — they look at what the user typed, not the result of a calculation. If you need to hide a section based on a total, get the user to enter the total directly instead
• Calculated fields are display-only — they can't be required because they're worked out from the other fields. Any "required" setting belongs on the input fields that feed the calculation, not on the calculated field itself

Next steps

• Showing fields only when needed — for the show/hide conditions that affect which fields feed a calculation.
• Organising forms with sections and pages — for the Repeating section that aggregations work over.
• Adding basic fields — for the Number and Currency input fields.