An additional installment means increasing the number of installments on a card purchase that is already on an installment plan — spreading a purchase currently split over 3 months across 8, for instance. Your monthly payment falls, but the installments are no longer interest-free: monthly interest accrues on the outstanding amount, and BSMV and KKDF are levied on that interest. This tool puts the new installment, the monthly relief and the total price of that relief side by side.
What this product is, and what it is not
This calculator models one transaction: increasing the installment count on a card purchase that is already installmented. Its starting point is a plan that already exists. Your total card debt, your other spending and the statement balance itself are not what is being spread.
- It calculates extending the installment count of an existing installment transaction.
- It does not calculate choosing installments at the point of purchase — that is a separate product.
- It does not calculate converting a full-price transaction into installments afterwards — use the credit card transaction installment tool for that.
- It does not calculate restructuring card debt — restructuring is a different regime under a different rate ceiling.
- Cash advances, late-payment interest and minimum-payment calculations are out of scope.
The four operations look alike but fall under different rate ceilings and different BDDK rules. Confusing this one with restructuring corrupts the result outright: restructuring is capped by the TCMB reference rate, whereas extending an installment plan is governed by the tiered maximum contractual rate. A calculation on the wrong regime rests on a rate your bank cannot lawfully apply here.
The current plan and the new plan
The tool measures the gap between two plans. Your current plan is taken as the transaction amount divided by the current installment count. The new plan spreads the same transaction amount across the new installment count you choose, with the applied monthly rate and the taxes on it.
The tool assumes your existing installment transaction is interest-free under a merchant campaign — that is, it computes your current monthly installment simply as amount divided by current installment count. If your current plan already carries interest, your real installment is higher than that, and the real "relief" is therefore smaller than shown here. Compare against the installment on your own statement.
The new installment count must be greater than the current one — otherwise there is no plan to extend, and the tool says so explicitly. The current count must be at least 2, because a single-payment transaction is not installmented at all; in that case the transaction installment tool is the right one.
Which interest rate applies
Credit card rates are not free. The TCMB publishes the maximum contractual rate applicable to credit card transactions, and banks cannot exceed that ceiling. The ceiling is not a single number: it is tiered by the card’s statement balance.
- Cards with a statement balance below 30,000 TL: a maximum contractual rate of 3.25% per month.
- Cards with a statement balance from 30,000 TL up to and including 180,000 TL: 3.75%.
- Cards with a statement balance above 180,000 TL: 4.25%.
What selects the tier is your card statement balance, not the amount of the transaction being extended. These are different figures: a 10,000 TL transaction on a card with a 200,000 TL statement balance sits in the 4.25% tier, not the 3.25% one. That is why the statement balance is a required field when the TCMB rate is selected, and why the tool never substitutes the transaction amount for it.
3.11% per month is the TCMB reference rate, and it is the contractual ceiling applied when card debt is RESTRUCTURED. An additional installment is not a restructuring — it is an ordinary re-spreading of an existing installment plan — so the governing ceiling is the tiered maximum contractual rate. A calculation built on 3.11% here rests on a rate your bank cannot apply to this operation and understates the cost.
Your bank may apply a rate below the legal ceiling. In that case choose to enter your own rate manually. If you also enter the statement balance, the tool checks whether your rate exceeds the legal ceiling for your tier and refuses the calculation if it does. Without the statement balance that check cannot be made, and the result says so plainly.
Transaction category and the maximum installment count
The BDDK limits card installment counts by spending category, and that limit applies to extensions too. The general ceiling is 12 months, rising to 18 for domestic travel and accommodation, 9 for groups such as health, furniture and appliances, 6 for tablets, 4 for electronics and 3 for jewelry. In several categories installments are prohibited entirely: telecommunications, fuel, food, cosmetics, purchases abroad, gift cards and others.
Where installments are prohibited, an existing installment transaction cannot be extended either; the tool refuses to calculate and states the reason. If you leave the category unspecified the arithmetic still runs, but the result declares that category-specific eligibility and the maximum count have not been verified. In that state 12 months is not a legally verified limit — installments may even be prohibited in your category.
How tax and funds enter the installment
Card interest carries 15% BSMV and 15% KKDF. Neither is levied on the principal: both apply only to the interest accruing that month, and both are folded into the installment. Every payment you make therefore has three parts — principal, interest, and the tax and fund on that interest. The result lists these separately, so you can see how much of the extra cost is interest and how much is tax.
Example: the trade-off between relief and price
Take a 24,650 TL purchase currently split over 3 installments. On the current plan your monthly payment is about 8,217 TL (24,650 / 3). Spreading it across 8 installments lowers the monthly payment markedly — but interest, BSMV and KKDF now accrue, and your total repayment rises above 24,650 TL.
The tool sums the trade-off in two rows: "Monthly Payment Relief" is what stays in your pocket each month, and "Cost of Extending" is the extra you pay in total for that relief. The "Cost Ratio" row expresses that extra as a percentage of the transaction amount and is the quickest way to compare scenarios. The more installments you add, the larger the monthly relief — and the larger the cost ratio.
Reading the result
- New Monthly Installment: what you will pay after the extension.
- Current Monthly Installment: today’s payment, on the interest-free assumption.
- Monthly Payment Relief: the gap between the two; your monthly cash-flow gain.
- New Total Repayment and Cost of Extending: the total price of the extension.
- Total Interest, BSMV and KKDF: the components of that price.
- Applied Monthly Rate and Rate Tier: which rate was used, and from which statement-balance tier.
- Applied BDDK Maximum Installments: the verified ceiling for your category — or the warning that it was not verified.
- New Payment Schedule: payment, principal, interest plus tax and remaining balance, month by month.
Limits and what is out of scope
Your bank may decline the request, apply a different rate below the legal ceiling, or add a transaction fee. On some cards and some campaign transactions an extension is not offered at all. Rely on your card statement and your bank for the binding figures.
- The calculation is for individual credit cards; corporate and commercial cards differ under both the TCMB tiers and the BDDK installment rules.
- The current plan is assumed interest-free; if you are extending an interest-bearing plan, the real relief is smaller.
- Transaction fees, card annual fees, insurance and campaign discounts are not included.
- Late-payment and minimum-payment scenarios are not modelled; the plan is assumed to be paid on schedule.
- Foreign transactions involving an exchange-rate difference fall outside this model.
Frequently Asked Questions
What is the difference between an additional installment and restructuring card debt?
An additional installment increases the number of installments on a single installmented purchase, and is governed by the tiered maximum contractual rate. Restructuring binds the whole of your card debt into a new plan and is capped by the TCMB reference rate of 3.11% per month. This tool calculates only the first.
Can I use this tool to installment a purchase I paid in full?
No. This tool extends a transaction that is already installmented, and it requires a current installment count of at least 2. To spread a full-price purchase into installments after the fact, use the credit card transaction installment tool.
Why do I have to enter my statement balance?
Because the TCMB maximum contractual rate is tiered by the card’s statement balance, and only that figure selects the correct tier. The transaction amount is a different quantity and cannot stand in for it, so the balance cannot be left blank when the TCMB rate is selected. If you enter your own rate the balance is optional — but supplying it lets the tool check your rate against the legal ceiling.
Can I extend to as many installments as I like?
No. The BDDK caps the installment count by spending category: 12 months in general, 18 for domestic travel and accommodation, 3–9 for several groups, and prohibited entirely for others. Select the category and the tool applies the limit; leave it unspecified and the tool reports that the calculation was not verified for your category.
My monthly payment falls — is that a gain?
Your monthly cash flow eases, but you pay more in total: interest, BSMV and KKDF accrue over the extended term. The "Cost of Extending" and "Cost Ratio" rows show that price. The decision is whether the relief is worth it to you.
My bank offers a rate below the ceiling — how do I calculate that?
Choose to enter your own rate and type in the monthly rate your bank quoted. If you also enter the statement balance, the tool confirms your rate does not exceed the legal ceiling for your tier. Enter a rate above the ceiling and the calculation is refused, because your bank cannot lawfully apply it.