loanTotalInterest()
Calculate total interest paid over the loan term (total repayments minus principal and commission) — use for “cost of borrowing” disclosures on finance landing pages.
Syntax
Every formula in Calcopolis must start with = in the Value field:
= loanTotalInterest(amount, interestRate, months, commission, installments)
| Part | Rule |
|---|---|
| Function name | loanTotalInterest — camelCase |
| Arguments | Same pattern as loanTotalCost |
| Return value | Interest portion only (excludes principal) |
Valid examples
= loanTotalInterest(loan_amount, interest_rate/100, term_months)
= roundTo(loanTotalInterest(loan_amount, interest_rate/100, term_months, 0.01), 2)
Invalid / unsupported
| Don't write | Why |
|---|---|
Expecting monthly interest |
This is total interest over the full term |
Parameters
| Argument | Description |
|---|---|
amount |
Loan principal. |
interestRate |
Annual rate as decimal. |
months |
Term in months. |
commission |
Fee as decimal of principal. Default 0. |
installments |
"EQUAL" or "DECREASING". Default "EQUAL". |
When to use loanTotalInterest()
Use when you need an explicit interest paid line:
| Situation | What loanTotalInterest() does |
|---|---|
| Transparency | Show interest next to monthly payment |
| Shorter term wins | Compare total interest for 15 vs. 30 years |
| Rate shopping | Isolate interest from principal |
Total interest = [loanTotalCost()](/docs/reference/formulas/loan-total-cost-function/) − principal − commission fee (handled inside the function).
Practical examples (ecommerce & leads)
1. Standard disclosure trio
| Variable | Formula |
|---|---|
monthly_payment |
= roundTo(loanInstallmentAmount(loan_amount, interest_rate/100, term_months), 2) |
total_interest |
= roundTo(loanTotalInterest(loan_amount, interest_rate/100, term_months), 2) |
total_repaid |
= roundTo(loanTotalCost(loan_amount, interest_rate/100, term_months), 2) |
2. Interest saved with larger down payment
Run the same formulas with loan_amount reduced by down_payment in a second View Mode or scenario variables.
Where to use it
| Location | Supported |
|---|---|
| Result widget Value | Yes — = ... formulas |
| Standalone variable (Variables tab) | Yes |
| Number / other input default Value | Yes, if formula-driven |
| Visibility formula | Yes |
| Custom Text / Table cells | No — use {{ }} templates there, not = functions |
After editing, run Calculate (or enable Run calculation on load in project Options) to refresh results.
Related
- [
loanInstallmentAmount()](/docs/reference/formulas/loan-installment-amount-function/) - [
loanTotalCost()](/docs/reference/formulas/loan-total-cost-function/) - Understanding Formulas and Variables —
=syntax and variables - Building Your First Calculator — end-to-end quote calculator