Debt consolidation calculator

The response leads with new_payment and total_savings so a landing, advisor worksheet, or onboarding flow can show the cash-flow change and the lifetime interest delta from the same deterministic math that runs free in the browser and at $0.002 per successful API call. An empty debts list is rejected as invalid_input and is not billed.

What remaining interest means when several debts become one loan

Sum those remaining interest figures across every row in debts, then do the same math once for a new loan whose principal is the sum of the balances, whose rate is new_annual_rate, and whose term is new_term_months. total_savings is old remaining interest minus new lifetime interest. That delta can be negative: stretching a five-year mix of cards into a seven-year personal loan can raise lifetime interest even when the headline rate falls. monthly_savings is the change in the combined monthly outlay and is a separate number; a lower payment with a longer term often costs more interest. This endpoint isolates those two figures so a page can show both the budget relief and the true cost of stretching the calendar, without a full period-by-period amortization table.

Input contract, payment formula, and response fields

Optional decimals from zero to eight defaults to two for currency-style rounding. Currency-like fields use half-up rounding once from the closed-form payment. Zero rates are allowed and use payment equals principal over n. Send a JSON object with three required fields. debts is a non-empty array of at most thirty records; each record needs balance greater than zero (outstanding principal; aliases principal and amount), annual_rate greater than or equal to zero as a percent such that twenty-two point nine nine means twenty-two point nine nine percent per year (aliases apr and rate), and remaining_months as a positive integer from one to six hundred (aliases term_months and months). An empty debts list fails with invalid_input naming the field; that failure is not billed. new_annual_rate is the consolidation loan's nominal annual percent (aliases new_rate and consolidation_rate). new_term_months is the new loan's whole-month term from one to six hundred (aliases new_term and term_months). The engine forms a payment for every current debt, sums principal, old_payment, old_total_interest, and old_total_paid, then prices one new loan on the combined principal. Outputs include debt_count, principal, old_payment, new_payment, monthly_savings, old_total_interest, new_total_interest, total_savings, old_total_paid, new_total_paid, new_annual_rate, new_term_months, monthly_rate, and a short formula string. Missing fields, non-finite numbers, non-positive balances, negative rates, out-of-range integers, and more than thirty debts fail with invalid_input.

Where a debt consolidation calculator earns its keep

Fintech onboarding and refinance funnels pre-fill debts from linked accounts and must return a deterministic consolidation quote without standing up a servicing core. Keep debts small, pin the rounded savings in tests, and you get reproducible quotes for education pages, worksheets, and edge workers. Credit counselors and advisors run side-by-side quotes—same balances, different new_annual_rate or new_term_months—to show when a longer term buys a lower payment at the cost of extra interest. Classroom and exam tools teaching consumer credit can pin rounded new_payment and total_savings against textbook amortizations. Comparison sites sweep new_term_months to chart the trade-off between monthly cash flow and lifetime interest. This tool does not underwrite credit, compute APR under Regulation Z, add origination fees or prepayment penalties, or simulate revolving minimums that change with balance; it prices remaining interest on the given remaining_months schedules against one new fully amortizing loan.