Installment Calculator
Calculate payment plan installments, interest, and per-period costs
What Is an Installment Calculator?
An installment calculator lays out the real cost of paying for a purchase in regular payments. You enter the price, any down payment, the interest rate, the number of installments, and the payment cadence — monthly, bi-weekly, or weekly — and it returns the amount due each period, the total interest, the all-in final cost, and a complete schedule of payments. It fits the payment plans offered on electronics, furniture, appliances, and online checkouts, where the advertised per-month figure tends to hide the total you will actually pay. Running the numbers here takes seconds, and switching between monthly, bi-weekly, and weekly plans shows instantly how the cadence changes the cost.
What this tool can do
- 🏷️ Price, down payment, and financed amount kept clearly separate.
- 📆 Three payment cadences: monthly, bi-weekly, or weekly.
- 🧾 Per-period payment, total interest, and the total cost of the purchase.
- 📋 A full schedule showing payment, interest, principal, and remaining balance for each period.
- 🆓 Interest-free plans supported — the financed amount is simply divided evenly.
- 🛡️ A down payment larger than the price is capped automatically.
When would you use it
- 🛍️ Buying a phone or laptop on a store’s payment plan and wanting the true cost.
- 🛋️ Comparing six-month and twelve-month installment plans for furniture.
- 💳 Deciding whether the upfront discount is worth paying in full.
- 📆 Budgeting a weekly or bi-weekly plan to match a pay schedule.
The calculation happens entirely in the browser; purchase figures stay on your device and are never saved anywhere. What the model assumes: a flat annual rate applied evenly across periods. Real store plans may carry service fees, insurance, or a final balloon payment, so check the contract’s small print — the calculator shows the arithmetic, not the fine print.
Last updated · 2026-09-01
Flat rate versus true APR
- A flat 6% instalment plan charges interest on the FULL principal even while you repay monthly — the true APR lands near double that figure.
- True APR solves for the rate equating all payments to today’s principal — that is what makes offers comparable.
- Zero-interest plans hide fees elsewhere: compare total outlay, not the headline rate.
The instalment price is not the loan price
Down payment and financed amount
Enter the price and any down payment, and the financed amount is shown as its own result — the figure interest is actually charged on, before any per-period payment appears.
Monthly, bi-weekly or weekly plans
Choose the payment cadence — monthly, bi-weekly or weekly — and the same purchase is priced on each rhythm, so store plans at different intervals compare fairly.
Schedule behind the per-period price
A full schedule lists every period's payment, principal, interest and remaining balance, alongside the total interest and all-in cost — the total the advertised per-month figure tends to hide.
Frequently asked questions
What's the difference between this and a loan calculator?⌄
An installment calculator is for retail purchase plans (like buy-now-pay-later or store financing), where you pay a down payment upfront and the rest in installments. A loan calculator is for bank loans where you receive the full amount up front and repay over time.
Does this handle interest-free (0% APR) plans?⌄
Yes — set the annual interest rate to 0 and the calculator will simply divide the financed amount equally across periods, with no interest charged.
How accurate is the payment schedule?⌄
It uses the standard amortization formula used by most lenders. However, actual offers from lenders may include fees, insurance, or other charges not captured here — always check your specific contract terms.
Why does a flat 6% feel far more expensive over time?⌄
Because interest keeps accruing on money you have already returned. On typical terms a flat rate on the original balance behaves like an APR of roughly 1.8–2 times its size — convert before comparing with bank loans.
Related tools
Related tools
Mortgage Calculator
Equal-installment and equal-principal amortization with full payment schedule
Loan Calculator
Calculate monthly payments, total interest and full cost for personal, auto and consumer loans
Compound Interest Calculator
Project investment growth with compound interest, regular contributions, and annual breakdown