Formulas

A formula is an expression like add(strength, intelligence) or years_since(birth_date) that produces a value from this entity’s other fields. The system computes the result whenever the entity is shown.

Formulas are the most flexible kind of auto-calculated field. You can do maths, string formatting, date arithmetic, and conditional logic — all from a small set of built-in functions.

Writing a formula

Formulas live in the Formula field of the auto-calculate behaviour editor. The editor shows you a function picker on the right; click any function to insert it at the cursor.

The shape is always the same: a function name, an opening parenthesis, arguments separated by commas, and a closing parenthesis.

add(strength, intelligence)
multiply(base_value, 2)
years_since(birth_date)

You can nest functions inside each other:

divide(add(a, b), 2)         // average of a and b
round(multiply(price, 1.07)) // price plus 7%, rounded

To reference a field on this entity, just type its identifier — strength, birth_date, etc. (No braces, no quotes.)

For text values, wrap them in quotes:

concat(first_name, " ", last_name)

For numbers, type them as-is: 2, 0.5, -7.

Live syntax checking

The editor checks your formula as you type. You’ll see one of three things under the formula box:

• Nothing — looks fine.
• “Checking syntax…” — the editor is asking the server.
• A red error message — describes what’s wrong (e.g. “Unknown function: bogus” or “Unbalanced parentheses”). Save is blocked until you fix it.

The check runs about half a second after you stop typing, so quick edits don’t spam the server.

Common patterns

A few formulas you’ll reach for again and again:

Goal	Formula
Sum of two stats	add(strength, intelligence)
Difference	subtract(max_health, current_health)
Percentage	multiply(divide(current, max), 100)
Round a result	round(divide(total, count))
Pick one of two values	if(is_active, bonus, 0)
First non-empty	coalesce(nickname, first_name, "Unknown")
Years between dates	years_since(birth_date)
Days between dates	days_between(start_date, end_date)

All 32 functions

Functions are grouped by what they do. Click into the editor’s function picker to insert any of them with placeholder arguments.

Maths

Function	What it does	Example
add(a, b, ...)	Add two or more numbers.	add(strength, intelligence)
subtract(a, b)	First minus second.	subtract(max_hp, current_hp)
multiply(a, b, ...)	Multiply two or more numbers.	multiply(price, quantity)
divide(a, b)	First divided by second.	divide(total_xp, level)
power(base, exponent)	Raise a number to a power.	power(level, 2)
sqrt(x)	Square root.	sqrt(damage)
abs(x)	Absolute value.	abs(temperature_delta)

Rounding

Function	What it does	Example
round(x)	Round to nearest whole number.	round(average)
floor(x)	Round down.	floor(divide(xp, 1000))
ceil(x)	Round up.	ceil(required_materials)
mod(a, b)	Remainder after division.	mod(day_number, 7)

Picking the largest, smallest, or summary

Function	What it does	Example
min(a, b, ...)	Smallest of the inputs.	min(health, stamina, mana)
max(a, b, ...)	Largest of the inputs.	max(base_dmg, modified_dmg)
sum(a, b, ...)	Add all the inputs.	sum(str, dex, con, int, wis, cha)
avg(a, b, ...)	Average of the inputs.	avg(test1, test2, test3)
count(a, b, ...)	How many of the inputs aren’t empty.	count(skill1, skill2, skill3)

Text

Function	What it does	Example
concat(a, b, ...)	Stick strings together.	concat(first_name, " ", last_name)
upper(s)	Make uppercase.	upper(name)
lower(s)	Make lowercase.	lower(email)
trim(s)	Remove whitespace from start and end.	trim(user_input)
length(s)	Number of characters.	length(description)
substring(s, start, end)	Take a slice from index start up to index end.	substring(code, 0, 3)
replace(s, old, new)	Replace text in a string.	replace(text, "old", "new")

Dates

Function	What it does	Example
years_since(date)	Years from the date to now.	years_since(birth_date)
days_between(a, b)	Days between two dates.	days_between(start, end)
date_add_days(date, n)	Add days to a date.	date_add_days(start, 30)
date_add_months(date, n)	Add months to a date.	date_add_months(founded, 6)
date_format(date, fmt)	Format the date as a string.	date_format(birth_date, "%Y-%m-%d")

Note

Date functions work with calendar dates and real-world dates. For calendar dates, “years” and “days” are counted in your world’s calendar — not the real-world Gregorian year.

Conditionals and missing values

Function	What it does	Example
if(condition, then, else)	Pick one of two values based on a condition.	if(is_active, "Active", "Inactive")
coalesce(a, b, ...)	First value that isn’t empty.	coalesce(nickname, first_name, "Unknown")
is_null(x)	True when the value is empty.	is_null(optional_field)
is_not_null(x)	True when the value isn’t empty.	is_not_null(required_field)

Worked examples

A handful of complete formulas, with a note on what each one is for.

Computed age

You have a birth_date field, and you want an age field that updates as the in-world calendar advances:

years_since(birth_date)

The result is a whole number. Set the age field to read-only.

Full name with optional title

Characters might or might not have a title. You want display_name to read “Lord Tyrell Mormont” when there is one, “Tyrell Mormont” when there isn’t:

concat(coalesce(title, ""), if(is_null(title), "", " "), first_name, " ", last_name)

A bit hairy. The cleaner answer is usually a Template instead — formulas are great for maths, less elegant for variable text-stitching.

Effective health

Max HP minus damage taken, with a floor at zero:

max(0, subtract(max_hp, damage_taken))

Status from a flag

When a Yes/No field is enough to decide the value:

if(is_active, "Active", "Inactive")

if takes a true/false value as its first argument and returns one of two results. For a Yes/No field, use the field directly. For “is this empty”, use is_null or is_not_null.

Note

Formulas don’t support comparisons like less than 10 or equals “warrior” — there are no <, >, or == operators. If your branching depends on numeric ranges or matching specific text values, the right tool is a visibility rule that switches between different fields, not a formula.

Spell save DC

D&D-style:

add(8, proficiency_bonus, ability_modifier)

What can go wrong

A few things the syntax checker won’t catch:

Field renamed or deleted. If the formula references strength and you later rename the field to str, the formula stops resolving. The result becomes empty until you update the formula. The Behaviour editor flags this when you open it.

Numeric field is empty. A formula like add(strength, intelligence) returns nothing if either field is empty. Use coalesce(strength, 0) to default to zero.

Division by zero or empty. divide(total, count) returns nothing when count is zero or empty. Wrap so the divide only runs with a usable value: if(coalesce(count, 0), divide(total, count), 0). The coalesce defaults count to 0 when it’s empty, and if treats 0 as false — so the divide only runs when count is non-zero.

Reference to itself. A formula that uses its own field (age = add(age, 1)) creates a cycle. The system rejects the save with an error.

For the full list of “I saved it but it doesn’t work” cases, see Common Pitfalls.

Where to go next

Templates A simpler kind of calculation when you're stitching values into a sentence.

Common Pitfalls What each formula error message means and how to recover.

Auto-Calculated Fields Step back and pick the right calculation kind for what you want to do.