Form Forge’s Calculation field does math in real time based on other fields in the same form. Build a pricing calculator, a quote estimator, an order form with automatic totals, a loan payment calculator, a BMI calculator, or any other form that needs to compute a value from user input.
A calculation field has a Formula setting where you write an expression using {field_id} placeholders for other fields. Example:
{quantity} * {unit_price}When the user fills in the quantity and unit price fields, the calculation field auto-updates to show the total. The calculation runs in real time as the user types, so there’s no “Calculate” button — the result just appears.
+ addition- subtraction* multiplication/ division% modulo( ) parentheses for order of operationsround({value}, decimals) — round to a specific number of decimalsmin({a}, {b}) — return the smaller valuemax({a}, {b}) — return the larger valueabs({value}) — absolute valuesqrt({value}) — square rootif({condition}, {if_true}, {if_false}) — conditional expressionsUse the if function to change the formula based on other fields:
if({membership} == 'premium', {total} * 0.8, {total})This gives a 20% discount to members, full price to everyone else.
A service website lets users get a quote based on project size, urgency, and features:
{size} * {urgency_multiplier} + ({extras_count} * 200))The total updates live as the user clicks options.
round({weight} / (({height}/100) * ({height}/100)), 1)){a_qty} * 10 + {b_qty} * 25 + {c_qty} * 50){subtotal} * 0.1){subtotal} + {tax})Combined with Form Forge’s Stripe payment field, the total flows directly into the payment.
if({early_bird}, ({tickets} * {price}) * 0.9, {tickets} * {price}))Every calculation field supports a prefix (e.g., $, €, £) and a suffix (e.g., USD, /month). The prefix and suffix are display-only; the raw value passed to Stripe or stored in submissions is the number.
Control how many decimal places the result shows. Useful for currency (2 decimals) vs percentages (1 decimal) vs whole-number counters.
Automatic thousand separators based on locale — 1,234.56 for English, 1.234,56 for German, etc.
A calculation field can be hidden from the user and still compute a value. Useful when you need to pass a calculated total to a Stripe payment field but don’t want to clutter the form with “Subtotal” and “Tax” rows.
Calculation fields and Stripe payments work together naturally. Point the Stripe payment field’s amount at a calculation field’s ID, and the user’s charge is whatever the calculation produced. Change the formula or the input fields, and the charge updates without any extra configuration.
Calculations update instantly as the user types or makes selections. No “Calculate” button. No page refresh. The form feels alive.
The client-side formula evaluator is deterministic and handles edge cases (empty fields, zero values, division by zero) gracefully — the field shows a placeholder until the required inputs are filled in.
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The calculation field is included in every paid plan.