Field Calculations

Calculated fields turn your forms into interactive tools. Instead of collecting raw data and crunching numbers later, you can compute totals, scores, and dynamic values right inside the form as the respondent fills it out. Build pricing calculators, quiz scoring systems, order forms with running totals, and ROI estimators — all without writing a single line of backend code.

How Calculated Fields Work

A calculated field is a special field type that displays a computed value instead of accepting user input. You define a formula that references other fields in your form, and BttrForm evaluates it in real time as the respondent enters data. The computed result updates instantly, giving respondents immediate feedback.

To add a calculated field, open the field palette in the form builder and drag the "Calculation" field type onto your form. Click it to open the formula editor.

Formula Syntax

BttrForm formulas use a straightforward syntax that supports arithmetic operations, built-in functions, and field references.

Referencing Fields

Reference other fields by wrapping the field's variable name in curly braces. You can find and set a field's variable name in its settings panel under "Variable Name."

{quantity} * {unit_price}

Arithmetic Operators

Built-In Functions

BttrForm provides a library of functions for common calculations:

// Rounding
round({total}, 2)        // Round to 2 decimal places
ceil({shipping_weight})   // Round up to nearest integer
floor({discount_pct})     // Round down to nearest integer

// Aggregation
sum({item1}, {item2}, {item3})  // Sum of values
avg({score1}, {score2})          // Average of values
min({bid1}, {bid2}, {bid3})      // Minimum value
max({rating1}, {rating2})        // Maximum value

// Conditional
if({age} >= 18, "Adult", "Minor")          // If-then-else
if({total} > 100, {total} * 0.9, {total})  // 10% discount over $100

// Text
concat({first_name}, " ", {last_name})  // Join text
length({comment})                        // Character count

Practical Examples

Example 1: Order Form with Running Total

Build an order form where the total updates as the customer selects items and quantities.

Fields:

• product_price — Dropdown with values: Basic ($29), Pro ($79), Business ($199)
• quantity — Number field (min: 1, max: 100)
• discount_code — Text field (optional)

Calculated Fields:

// Subtotal
{product_price} * {quantity}

// Discount (10% if code is "SAVE10", otherwise 0)
if({discount_code} == "SAVE10", {subtotal} * 0.10, 0)

// Tax (8.5%)
({subtotal} - {discount}) * 0.085

// Grand Total
round({subtotal} - {discount} + {tax}, 2)

The respondent sees the subtotal, discount, tax, and grand total update instantly as they change their selections.

Example 2: Quiz Scoring

Create a self-grading quiz that shows the respondent their score at the end.

Fields:

• q1 — Radio: "What is 2 + 2?" (Options: 3, 4, 5)
• q2 — Radio: "Capital of France?" (Options: London, Paris, Berlin)
• q3 — Radio: "Largest ocean?" (Options: Atlantic, Pacific, Indian)

Calculated Fields:

// Individual question scores
// Each correct answer = 1 point
{q1_score}: if({q1} == "4", 1, 0)
{q2_score}: if({q2} == "Paris", 1, 0)
{q3_score}: if({q3} == "Pacific", 1, 0)

// Total score
{total_score}: sum({q1_score}, {q2_score}, {q3_score})

// Percentage
{percentage}: round(({total_score} / 3) * 100, 0)

// Result message
{result}: if({percentage} >= 70, "Pass!", "Keep studying!")

Example 3: Pricing Calculator

Let prospects estimate their monthly cost based on their expected usage.

Fields:

• plan — Radio: Free, Pro ($29/mo), Business ($79/mo)
• extra_responses — Number: additional responses beyond plan limit
• extra_storage — Number: additional storage in GB

Calculated Fields:

// Base price from plan selection
{base_price}: if({plan} == "Free", 0, if({plan} == "Pro", 29, 79))

// Overage costs
{response_cost}: max({extra_responses} - 1000, 0) * 0.01
{storage_cost}: max({extra_storage} - 1, 0) * 2

// Estimated monthly total
{monthly_total}: round({base_price} + {response_cost} + {storage_cost}, 2)

Formatting Calculated Results

By default, calculated fields display raw numbers. You can configure formatting in the field settings:

• Currency — prefix with $, EUR, or INR symbol and use two decimal places
• Percentage — append % and round to the nearest integer
• Number — set decimal places and thousand separators
• Text — display the result as plain text (useful for conditional messages)

Select the appropriate format in the "Display Format" dropdown of the calculated field's settings panel.

Chaining Calculations

Calculated fields can reference other calculated fields, allowing you to build complex computation chains. BttrForm automatically determines the evaluation order based on dependencies.

{subtotal}:    {quantity} * {unit_price}
{tax}:         {subtotal} * 0.085
{shipping}:    if({subtotal} > 50, 0, 9.99)
{grand_total}: {subtotal} + {tax} + {shipping}

Using Calculations in Logic Rules

Calculated field values can be used as conditions in both show/hide rules and skip logic. This is powerful for scenarios like:

• Show a "Volume Discount" message when the calculated subtotal exceeds $500
• Skip to a "Premium Support" page when the selected plan's calculated price is above $100
• Hide the checkout page when the grand total equals zero (free tier, no overages)

Troubleshooting

Formula shows NaN: A referenced field is empty or contains non-numeric text. Wrap the reference in a fallback: if({field} == "", 0, {field}).

Decimal precision issues: Floating-point math can produce results like 29.990000000001. Use round({result}, 2) to clean up display values.

Calculation not updating: Ensure the source fields have variable names assigned. Fields without variable names cannot be referenced in formulas.