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Installment Payment Calculator — how much is the monthly payment?
Buying on installments is a popular financing method that spreads the cost of a larger purchase into convenient monthly payments. Shops, banks, and financial institutions offer both interest-free (0%) and interest-bearing installment plans. The installment payment calculator lets you quickly compute the monthly payment and total amount you will pay. Simply enter the purchase price, number of installments, and annual interest rate — the calculator instantly shows your monthly payment and total cost. With 0% interest, the monthly payment is a simple division. With interest greater than 0%, the annuity formula is applied, which accounts for accumulating interest and determines a fixed monthly payment for the entire repayment period. This tool is useful for comparing installment offers from different retailers and banks — enter the parameters of each offer and see which one is cheaper.
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How the installment payment calculator works
The calculator uses two calculation paths: 1. Interest rate = 0%: payment = round(amount / number_of_installments, 2) total repayment = amount interest cost = 0 2. Interest rate > 0% (annuity formula): r = annual_interest_rate / 100 / 12 payment = round(amount × r × (1+r)^n / ((1+r)^n − 1), 2) total repayment = round(payment × n, 2) interest cost = round(total_repayment − amount, 2) All results are rounded to the nearest grosz (2 decimal places).
Example: PLN 3,000 over 12 installments at 12% per annum
Amount: PLN 3,000. Number of installments: 12. Interest rate: 12% per annum (1% per month). Monthly rate r = 0.01. Payment = 3,000 × 0.01 × 1.01^12 / (1.01^12 − 1) ≈ PLN 266.43. Total repayment: 266.43 × 12 = PLN 3,197.16. Interest cost: PLN 197.16. At 0% interest: payment = 3,000 / 12 = PLN 250, total = PLN 3,000, interest = PLN 0.
Frequently asked questions
How is the monthly installment payment calculated?
With 0% interest, the monthly payment is simply the purchase price divided by the number of installments. With interest above 0%, the annuity formula is used: payment = amount × [r × (1+r)^n] / [(1+r)^n − 1], where r is the monthly interest rate (annual rate / 12) and n is the number of payments.
What is the difference between 0% installments and interest-bearing installments?
0% installments mean no additional financial cost — you pay exactly the price of the product, divided into equal monthly payments. Interest-bearing installments include an interest charge, so the total repayment exceeds the purchase price.
What is the interest cost shown in the calculator?
The interest cost is the difference between the total repayment (sum of all monthly payments) and the original purchase price. It represents the total interest expense you will pay at the chosen rate and number of installments.
How many installments can I choose in the calculator?
The calculator supports between 2 and 120 monthly installments, covering repayment periods from 2 months to 10 years. Typical retail installment plans are 3, 6, 10, 12, 24, or 36 months.
Are shop installment plans genuinely interest-free?
0% installment plans at retailers may carry hidden costs such as mandatory insurance or arrangement fees. Always check the APR (Annual Percentage Rate) disclosed by the retailer or bank, which captures all costs.
How do I compare installment offers from different retailers?
The best way to compare installment offers is by APR and total amount repayable. Use the calculator with the amount, number of installments, and interest rate of each offer — the "Total repayment" figure shows what you will pay overall.
Do I always pay more with more installments?
Yes, when the interest rate is above 0% — the more installments, the longer interest accumulates and the higher the total interest cost. With 0% interest, the total repayment stays the same regardless of the number of installments.
What is the annuity payment formula?
The annuity formula calculates a fixed monthly payment that covers both principal and interest. At the start of repayment, a larger share of each payment is interest; over time the principal share grows. The monthly payment amount remains constant throughout the repayment period.
Does the calculator include fees and insurance?
The calculator computes the payment based only on the principal amount, number of installments, and nominal interest rate. It does not include arrangement fees, insurance premiums, or other charges. Use the APR provided by the financial institution for a full cost comparison.
How do I choose the optimal number of installments?
The optimal number of installments depends on your monthly budget. More installments mean a lower monthly payment but a higher total interest cost at rates above 0%. Choose as many installments as comfortably fits your budget while minimising the total interest paid.
Results are for informational purposes only. The calculator computes payments based on nominal annual interest rate only and does not account for arrangement fees, insurance, or other additional costs. Check the APR (Annual Percentage Rate) provided by the financial institution for the true cost of credit.
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Monthly paymentPLN 250.00Monthly payment
- Total repayment
- PLN 3,000.00
- Interest cost
- PLN 0.00