Tecof • September 16, 2026
Instalment Sales and the Term Difference: Effect on Profit Margin
In Brief
Instalment selling is a form of sale in which the customer splits payment across months while the merchant receives the money with commission and term costs already deducted. The term difference, or vade farkı, is the price of that split: the bill the merchant receives for taking money spread over months instead of in one lump today. In Turkey instalments stopped being a payment convenience long ago and became part of price competition; that is why in most stores the instalment decision is taken on the marketing side while its cost shows up in accounting two months later. As of 2026 the question is not "should we offer instalments" but "do we know how much margin each instalment count erodes on which product".
Thursday afternoon, 14.40. The month-end close of a small appliances store shows an odd picture: revenue is up 18 percent on the previous month, average basket has risen from 2,340 TL to 3,110 TL, and order count is nearly unchanged. Against that, the ratio of net cash landing in the bank account to revenue has fallen from 91.4 percent to 86.2 percent. The advertising budget has not changed, the return rate has not changed, the shipping agreement has not changed.
The only thing that changed was the instalment option on the site being raised from 6 to 9 at the start of the month. The basket grew, because the customer looked at the monthly payment and chose the more expensive model. But on every 9-instalment transaction the share left with the bank rose noticeably compared with 6, and none of that difference was reflected in any price tag. The store had taken the decision that grew revenue and the decision that shrank margin at the same moment, and was reporting only the first. The whole instalment debate knots at this point: instalments are a marketing instrument, but their cost is a financing line item, and the two sit in different tables.
1. How Does Money Flow in an Instalment Sale?
In an instalment sale the customer splits the money across months while the merchant receives it in one go but reduced; banks and payment institutions share the difference. No margin calculation can be built without knowing the detail behind that sentence, because where the deduction occurs is not the same in every store.
Who is in the chain?
- Issuing bank: the bank that issued the customer's card. It is the party that actually grants the instalment facility and collects from the customer across months.
- Acquiring bank: the bank through which the store collects. It pays the sale amount to the merchant and takes a commission in return.
- Payment institution or virtual POS provider: the technical and commercial layer between the site and the banks; it lets you open several banks' instalments through one integration and takes its own share for that.
- Card scheme: the network running the rules and clearing infrastructure of the transaction; it does not bill you directly but sits inside the total commission.
The practical consequence: what you call "the commission rate" is not one number but the sum of three items. When choosing a virtual POS provider, asking how those three separate out is more useful than hearing a single percentage; we handled these items provider by provider in our virtual POS comparison article.
Commission, term cost and settlement holds
The cost of an instalment transaction has two parts: the base commission taken on every transaction, and the term cost added as the instalment count rises. Single-payment commission is usually fixed within a band; the additional rate stacked on top as instalments increase grows almost linearly. The reason is simple: if the bank will collect from the customer over nine months but pays you today, it is carrying the financing cost of that gap and passes it into the commission.
There is a third item, and in most contracts it sits in the small print:
- Settlement hold (valör): the number of days before the sale amount reaches your account. It is kept long in sectors seen as risky and for newly opened merchant accounts.
- Deduction timing: whether commission is taken at the moment of the transaction or at payout; it directly affects accounting reconciliation.
- Payout form on instalment transactions: in some agreements the full amount is paid at once, in others it lands instalment by instalment. The second completely changes cash flow.
Revenue and collection are not the same thing
The most commonly missed effect of instalment selling is not in profit but in cash. Two months of the same size are not the same month for the business if their collection calendars differ. The table below shows, as an example scenario, when 100,000 TL of daily revenue turns into cash under different agreement structures.
| Agreement type | Cash arrival | Effect on restocking | Who sees it |
|---|---|---|---|
| Single payment, short hold | Full amount within a few business days | Unconstrained | Established merchants |
| Instalment, paid at once | Full amount at end of hold | Unconstrained, margin lower | Common e-commerce agreement |
| Instalment, paid per instalment | Spread across months | Squeezed | New or higher-risk merchants |
| Long settlement hold | Full amount, delayed | Seriously squeezed | High-return categories |
A store working under the third row can become unable to buy stock while being profitable on paper. That is why the payout clause in the contract matters as much as the commission rate, and it is open to negotiation.
2. What Is the Term Difference, and Who Pays It?
The term difference is the price gap created when an amount is paid over time rather than up front; in instalment selling either the merchant absorbs it, passes it to the customer, or the two share it. Which model the decision is made under directly determines the figure that appears in the profit table.
Three models and their consequences
In practice you meet three structures. Which is right depends on the product's margin and the competition in the category; there is no universal answer.
| Model | What the customer sees | Effect on margin | When it fits |
|---|---|---|---|
| Merchant absorbs | Same price, "no term difference" | Erodes directly with instalment count | High-margin products in fierce competition |
| Passed to customer | Higher total when paying in instalments | Protected | Low-margin products where price transparency is expected |
| Shared above a threshold | No difference up to a set instalment count | Controlled erosion | Catalogues with a wide price range |
| Bank-supported campaign | No difference, limited to the campaign period | Part of the cost sits with the bank | Campaign periods and selected categories |
What to watch in price display
If the term difference is passed to the customer, the cash price and the instalment total must both be clearly visible on the purchase screen. Showing the monthly instalment large and the total small may look like it lifts conversion in the short term, but it raises return and dispute rates. We covered in detail how missing information at the payment step turns into cart abandonment in our article on conversion rate.
Documentation and regulation
How the term difference is shown on the invoice, which base it enters and which rate applies are matters of tax legislation, and the detail of application can change over time. What is described here is the mechanism: the term difference arises as part of the sale price, so it must be documented, and tracking it separately in the accounting record works in your favour. Verify the current form of the obligation that applies to your own situation with your accountant. We explained the e-commerce side of setting up document flow in our article on e-invoicing and e-Arşiv.
3. How Do You Calculate the Effect on Profit Margin?
The effect of instalments on margin is a single subtraction: take the total payment cost ratio away from the gross margin ratio, and what remains is your real margin. The difficulty is not in the arithmetic but in being able to see the total payment cost as one percentage.
The formula to use
- Gross margin: (sale price − product cost) ÷ sale price. Shipping, packaging and the return provision are not yet deducted.
- Total payment cost: base commission + instalment term rate + any fixed per-transaction fee. Express all of it as a ratio of the sale price.
- Net contribution margin: gross margin − payment cost − shipping provision − return provision − packaging. This is the real share the order leaves with the business.
- Break-even instalment count: the instalment count at which net contribution falls to zero. Knowing this number for each category is the foundation of an instalment policy.
An example scenario
The table below is purely illustrative; the figures come from no real agreement and were chosen to show how the calculation is built. Say the sale price is 4,000 TL, product cost 2,800 TL, shipping and packaging 120 TL, and the return provision 2 percent of the sale price. Gross margin is 30 percent.
| Instalments | Assumed total payment cost | Payment cost (TL) | Net contribution (TL) | Net contribution rate |
|---|---|---|---|---|
| Single payment | 2.0% | 80 | 920 | 23.0% |
| 3 instalments | 4.0% | 160 | 840 | 21.0% |
| 6 instalments | 6.5% | 260 | 740 | 18.5% |
| 9 instalments | 9.0% | 360 | 640 | 16.0% |
| 12 instalments | 11.5% | 460 | 540 | 13.5% |
What the table really shows is not the individual rows but the gap between them: in this scenario the difference between single payment and 12 instalments is 380 TL per order. In a store taking 500 orders a month, if the instalment mix shifted entirely to 12, that corresponds to a margin difference of 190,000 TL a month. No advertising optimisation offsets a line item of that size on its own.
Finding the break-even point
In categories with a low gross margin, long instalments are mathematically impossible. Had the gross margin in the scenario above been 15 percent instead of 30, net contribution would approach zero at 9 instalments and fall below zero at 12. That is why instalment policy is built per category, not across the whole catalogue. For every category, answer one question: how many instalments zero out net contribution here, and how many steps below that are we standing?
4. How Many Instalments for Which Product?
Instalments are worth their cost to the extent that they grow the basket; where they do not grow it, they are only a cost. Build the policy around that single test: does the instalment option genuinely change the purchase decision for this product?
The basket threshold
On low-value orders instalments change nothing, because the customer is already looking at an amount they could pay in one go. On high-value orders instalments can be a precondition of the purchase. The practical approach is to take your average basket as the threshold and limit instalment counts on orders below it. We gathered the other instruments for raising average basket in our AOV article; instalments are the most expensive of them, which is why they should be tried last.
Category and regulatory limits
In Turkey, the maximum instalment count on credit card sales and the prohibition of instalments in certain goods and service groups are set by regulatory decisions, and those limits are changed from time to time. What the software side needs to do is keep instalment counts as an adjustable, category-based field rather than hard-coding them; that way, when a limit changes you update it from one screen. Confirm which category falls into which class, and the current upper limit, with your bank and your accountant; displaying the wrong instalment count causes the transaction to be declined.
Bank-supported campaigns
During campaign periods banks offer extra instalments or deferral in selected categories and carry part of the cost. These are genuinely cheap instalment opportunities, but on two conditions: that campaign start and end dates are reflected correctly on the site, and that the display changes automatically for cards outside the campaign. Stores that manage this by hand keep showing difference-free instalments after the campaign ends and pay the difference themselves.
| Basket value | Suggested approach | Term difference | Rationale |
|---|---|---|---|
| Below average | Single payment or 2-3 instalments | Merchant absorbs | Instalments change nothing, the cost is wasted |
| Average band | 3-6 instalments | Merchant absorbs | Contribution to conversion is measurable |
| Twice the average | 6-9 instalments | Shared above a threshold | Monthly payment perception becomes decisive |
| High value | Maximum instalments | Passed to customer or campaign-backed | The sale may not happen without instalments |
5. Operations: Virtual POS, Accounting and Returns
Even with the right instalment policy, three operational details can take the gain back: the structure of the commission agreement, accounting reconciliation, and how returns are processed.
What to negotiate in the agreement
- Band-based rates: instead of one "instalment transaction rate", ask for separate rates for the 2-3, 4-6, 7-9 and 10-12 bands; banded structures lower total cost in most stores.
- Settlement hold period: shortening it can be requested as revenue grows; its effect on cash flow is worth as much as a commission discount.
- Payout report format: ask for a report that breaks commission down transaction by transaction. Margin analysis cannot be done from a report that arrives as a lump sum.
- Return commission: put in writing whether commission is refunded on a returned transaction; if it is not, it is a hidden cost line in high-return categories.
Accounting reconciliation
The accounting problem with instalment selling is that one order appears not as a single line but as amounts arriving on different dates. If there is no field matching the order number to the bank payout record, at month-end you cannot find which order paid how much commission, and the margin report turns into guesswork. Infrastructure that builds this match automatically saves weeks on the accounting side by itself; when choosing an e-commerce platform, put the presence of a payment reconciliation report on your checklist.
Returns, cancellations and disputes
On an instalment transaction, a refund is generally reflected to the customer's card under the instalment structure of the original transaction; that is, the customer does not get the money back in one go. This is one of the biggest generators of customer complaints and needs a one-sentence explanation on your returns page. On the merchant side the critical question is whether the commission paid comes back. In high-return categories this item is a second burden on top of the instalment cost and must be included in the margin calculation.
6. Measurement: Seeing the Real Cost of Instalments
Unless it is measured, instalment cost always looks smaller than it is, because it does not sit as one expense line but is scattered inside every order. Three reports make it visible.
Margin report split by instalment count
Once a month, group orders by instalment count and write, for each group, the average basket, the payment cost and the net contribution. In most stores two things surface the first time this table is built: the share of instalment orders is higher than assumed, and the net contribution of the long-instalment group is lower than expected.
Basket and conversion effect
Whether the instalment cost is justified can only be understood alongside basket and conversion, not margin alone. The right question: when we raised the instalment option by one step, how much did average basket and conversion rate move? The only honest way to measure this is to compare two groups in the same period; comparing last month with this month misleads, because campaign and seasonal effects sit in between.
Cash flow projection
When the instalment mix changes, the calendar of cash arrival changes with it. Build the next three months' cash projection together with an assumption about the instalment mix. In heavy campaign periods especially, stock payments can be squeezed because the revenue increase turns into cash months later; this is the financing problem profitable stores run into most often.
Building an Instalment Policy in Thirty Days
Thirty days is enough to move instalment policy from instinct to arithmetic. The order matters: do not change anything before measuring, because you can only read the effect of a change against the earlier table.
Days 1-7: map the current state
Break down the last three months of orders by instalment count. Write each group's order count, revenue share and average basket. Pull the actual commission amounts from the virtual POS payout reports and compare them with the contracted rate; the two failing to match is more common than assumed. Nothing is changed this week.
Days 8-14: break-even by category
For your twenty best-selling categories, calculate gross margin, shipping and return provisions, and net contribution. Find the break-even instalment count for each. Split the resulting list into two columns: categories where instalments are viable, and categories whose margin will not carry them. The second column is usually more crowded than anyone expects.
Days 15-21: apply the policy
Reset instalment counts by category and basket threshold. Decide above which threshold the term difference passes to the customer, and show the cash price and the instalment total together on the payment screen. Hold the banded-rate conversation with your virtual POS provider this week; with the breakdown report freshly in hand, your negotiating ground is strong.
Days 22-30: measure and lock it in
Track conversion rate, average basket and instalment mix weekly after the change. Set the instalment-split margin report to run automatically each month. Update the cash projection with the new instalment mix and put the next review date in the calendar; regulatory changes and campaign periods require reopening this policy a few times a year.
Here is the job for tomorrow morning: group the last 90 days of orders by instalment count and write only two columns — revenue share per group and payment commission amount per group. If the longest instalment group's revenue share exceeds 20 percent and its commission share is clearly higher than its revenue share, you have found the item eroding your margin; fixing it is faster than designing a campaign, because it lives in a single settings screen.
Frequently Asked Questions
Who pays the commission on an instalment sale?
The merchant pays it; the bank deducts it from the sale amount and transfers the remainder to the merchant's account. The customer pays nothing extra unless the merchant passes the term difference into the price. That is why "instalments with no term difference" is a product that is free for the customer and costly for the merchant.
Are the term difference and interest the same thing?
No. The term difference is the part of the sale price that increases with the payment term and is part of the sale transaction; interest is the return on a credit relationship. They are treated differently for accounting and documentation, so they need to be classified correctly on the invoice and in the records. Clarify the correct classification for your own transactions with your accountant.
How many instalments should I offer?
As many as the category's gross margin can carry. Calculate the instalment count that zeroes net contribution and stay at least two steps below it. Applying one instalment count across the whole catalogue means missing the opportunity on high-margin products and losing money on low-margin ones.
Do instalments really raise average basket?
On high-value products they usually do; on low-value ones they make no difference. Rather than assuming, measure it: changing the instalment option in one category only and comparing it with other categories in the same period is the cleanest method.
Does passing the term difference to the customer hurt conversion?
When the cash price and the instalment total are shown clearly, the drop stays limited; the real problem is the difference appearing as a surprise at the payment step. Cart abandonment rises noticeably in stores that show the total for the first time on the payment screen rather than on the product page.
When does the money from an instalment sale reach my account?
It depends on the payout structure in your agreement. In common e-commerce agreements the full amount is paid at once at the end of the settlement hold; in some agreements it lands instalment by instalment. Ask about this clause explicitly before signing, because it can affect cash flow more than the commission rate does.
How does a customer get refunded on a returned instalment order?
The refund is generally reflected to the card under the transaction's instalment structure, meaning the customer gets the amount back spread over months rather than at once. Explaining this in one sentence on your returns page and in your return confirmation email removes a significant share of the questions reaching customer service.
Can I offer instalments in every category?
No. The maximum instalment count on credit card sales and the goods and service groups where instalments are not permitted are set by regulatory decisions, and these change from period to period. Keep the instalment setting on your site category-based and easy to update, and confirm the current limit with your bank.
How do I compare the cost of cash on delivery with instalment selling?
They are built from different items: in instalment selling the cost is commission and the term difference, while in cash on delivery it is the collection service fee, the return rate and the cost of undelivered orders. The correct comparison runs both through net contribution per order, not by placing the percentages side by side.
What do I need in order to report instalment cost?
At minimum, a payout report that breaks commission down per order, and infrastructure that can match that report to the order number. Without those two, the margin report rests on estimates. Ask for the report format up front when choosing a provider; changing it after the contract is often not possible.