This interview is with Cem Oner, Founder / Finance & Public Data Publisher, hesapcebimde.com.
To kick things off, how would you introduce yourself to readers as the Founder and Finance & Public Data Publisher behind HesapCebimde.com, and what kinds of real-world problems your calculators are built to solve in Turkey?
I’m Cem Öner, the founder and Finance & Public Data Publisher behind HesapCebimde.com. Before building the platform, I spent 15 years in finance management, where I repeatedly saw people given a final number without being shown how it was calculated, which costs were excluded, or what could change the result.
HesapCebimde turns those everyday financial questions into practical calculators built around Turkish rules and real-life decisions. The tools cover areas such as:
- loan payments
- taxes
- salaries
- severance pay
- rent increases
- inflation
- vehicle costs
- household budgeting
The aim is not simply to say, “Your monthly payment is this.” We also show the formula, total cost, taxes, common mistakes and the official data behind the calculation.
A loan can appear affordable when someone looks only at the monthly installment, while fees, taxes and total repayment tell a very different story. HesapCebimde was built to make those hidden consequences visible before the user commits money or makes an important decision.
What path led you from finance operations into publishing public-data-driven tools, and which moment or lesson most shaped how you design and maintain calculators for the Turkish market?
My path began in finance operations, where I spent 15 years working with cash flow, loans, taxes, payroll, invoices, and management reporting. I repeatedly saw people making important decisions based on a single number—usually a monthly payment or an expected return—without seeing the taxes, fees, assumptions, or downside scenario behind it. HesapCebimde grew from the idea that these calculations should be understandable and accessible before someone commits money.
One experience particularly shaped my approach. I discovered that the same customer had been created under two separate account records. Each record looked correct on its own, but neither showed the customer’s true balance. It taught me that a clean-looking result can still be misleading when the underlying data, definitions, or context are incomplete.
That lesson now guides how I design and maintain calculators for Turkey. I try to show not only the answer but also:
- the formula
- the official source
- the update date
- common mistake
- hidden cost
Turkish rates and rules can change quickly, so each calculator must be treated as a maintained public-data product rather than a page that is published once and forgotten. The goal is to help users understand what could change their result, not simply give them a number that looks precise.
Focusing on KDV Hesaplama: what’s the most common real‑world edge case (e.g., tevkifat, mixed rates, VAT‑inclusive pricing) you had to engineer around, and what’s one practical tip SMEs can use to avoid miscalculating KDV on invoices?
The most common edge case was not an unusual KDV rule but VAT-inclusive pricing. In real invoices and quotations, people often know the final amount but forget that the tax is already inside it. For example, multiplying a KDV-inclusive price of 120,000 TL by 20% produces 24,000 TL, even though the correct KDV is 20,000 TL and the underlying taxable amount is 100,000 TL. That is why the calculator makes users choose the calculation direction first: add KDV to a net amount or extract KDV from a gross amount.
My practical tip for SMEs is to state “KDV dahil” or “KDV hariç” explicitly on every quotation, contract, and invoice line before calculating anything. Where an invoice contains products subject to different rates, calculate each rate group separately rather than applying one average rate to the total. This prevents both mathematical errors and later disagreements over which party was expected to absorb the tax.
The calculator and worked examples are available here: https://hesapcebimde.com/kdv-hesaplama
Shifting to Kredi Analizi: when you evaluate borrower risk for freelancers and micro‑SMEs with thin files, which signals from real bank statements, POS turnover, or e‑Defter records have proven most predictive in your experience, and what one practice should owners adopt before they apply?
For freelancers and micro-SMEs with thin credit files, I trust cash-flow behavior more than a single turnover figure. The strongest signals are:
- consistency between bank inflows, POS settlements, and e-Defter sales records;
- how concentrated revenue is among a few customers;
- whether tax, payroll, and supplier payments are made regularly;
- how much usable cash remains after existing loan payments.
High POS turnover alone can be misleading if it is seasonal, followed by frequent refunds, or if funds are transferred out of the business immediately.
One pattern I watch closely is whether reported sales can be reconciled across systems. If POS settlements, bank deposits, and accounting records tell different stories, the lender cannot easily distinguish growth from temporary or unexplained movement. I once found the same customer divided between two account records; each looked reasonable separately, but neither showed the true balance. Thin-file lending has the same problem: incomplete records can make a healthy business look risky, or a weak one look stronger than it is.
The best practice before applying is to separate business and personal transactions and reconcile at least the previous 12 months into one simple cash-flow summary. Owners should be able to explain:
- recurring inflows;
- unusual transfers;
- seasonality;
- current debt payments; and
- the cash remaining after essential expenses.
A lender gains confidence when the records agree and every large movement has a clear business explanation.
On Maaş Tahmini: given frequent changes to brackets, exemptions, and social security thresholds, how do you keep net salary estimates realistic for both employers and candidates, and what’s the single input users most often get wrong that skews take‑home pay?
I keep salary estimates realistic by treating payroll as a dated calculation rather than a permanent formula. The model needs to reflect the applicable income tax brackets, minimum-wage exemptions, SGK contribution limits, stamp tax treatment, and the calculation month. I also separate the employee’s net salary from the employer’s total cost, because those two figures are often confused during hiring discussions.
The input users most often get wrong is the employee’s cumulative income tax base. Two people with the same monthly gross salary can receive different net amounts depending on previous earnings and whether they have already entered a higher tax bracket. Entering zero for someone who is already several months into the tax year can make the estimated take-home pay look much higher than the actual payroll result.
My practical approach is to show the assumptions and month-by-month change rather than presenting one net figure as guaranteed. The salary calculator is available here:
Regarding Damga Vergisi: which document types or clauses do you see misclassified most often in practice, and what simple verification step would you recommend to ensure the correct rate or ceiling is applied before signing?
The documents I see misclassified most often are agreements labeled as a “protocol,” “offer” or “undertaking,” even though their legal substance creates a binding monetary obligation. Fixed-term rental agreements are another common problem: businesses sometimes calculate stamp tax using one month’s rent rather than the total rent for the full contract period. Amendments, guarantees and additional commitments can also be overlooked when they create a separate taxable transaction inside the same document.
My practical recommendation is to complete a one-page verification before signing:
- Identify the document’s legal nature
- Determine the total monetary value
- Confirm the contract duration
- Count the number of taxable copies
- Check whether it contains more than one independent obligation
Only after that classification should the current rate and annual ceiling be applied. The document title alone should never determine the calculation.
The calculator and worked examples are available here:
When businesses budget for Icra Masrafı, which specific cost components (e.g., tebligat, başvuru harçları, avans, vekalet ücretleri) are most underestimated in your user data or case reviews, and what one planning tip helps decide between early settlement and formal enforcement?
The most underestimated costs are usually not the initial filing fee but the expenses that may follow.
These commonly underestimated components include:
- Repeated service attempts
- Address research
- Enforcement and sale advances
- Valuation
- Transport or storage costs
- The statutory attorney fee added to the file (which businesses often confuse with the separate fee arrangement they may have with their own lawyer)
My planning rule is to compare the expected net recovery under two scenarios before taking formal action:
- An early-settlement scenario that shows the amount and timing of a realistic settlement.
- A formal-enforcement scenario that includes interest, all enforcement costs, the debtor’s identifiable assets, the probability of collection, and how long the process may take.
A legally valid receivable is not automatically a collectible receivable.
When the debtor has no verified income or assets, spending more on enforcement may only increase the amount recorded on paper. When assets are visible and the settlement offer is materially below the likely net recovery, formal enforcement becomes easier to justify. The practical mistake is comparing the settlement offer with the headline debt rather than with the amount the business is realistically likely to collect after time and costs.
The calculator is available here: https://hesapcebimde.com/yasal-faiz-hesaplama
Because rates and rules change, what’s your playbook for sourcing, versioning, and QA‑testing public thresholds across KDV, payroll, stamp tax, and court fees so a calculator stays accurate the day a change goes live?
My playbook begins with a source hierarchy. I use the relevant law, official gazette, ministry, tax authority, or court tariff as the primary source, then record the publication date, effective date, affected calculation fields, and the exact source link. Secondary summaries are useful for finding a change, but they do not become the calculator’s legal basis.
I keep rates and thresholds in versioned data files rather than hard-coding them into page templates. Each record has an effective-from date, and the previous version remains available for historical calculations. This is especially important for payroll, where tax brackets, exemptions, and contribution ceilings may change at different times, while KDV rates or court fees may apply according to the transaction date.
Before a change goes live, I test known manual examples around the boundaries: one amount just below the threshold, one exactly at it, and one just above it. I also compare the output with the previous version to confirm that only the intended calculations changed. For high-impact updates, I run the new data in parallel before switching to production.
The final QA step is a second review of the source, assumptions, and displayed explanation. My rule is that a calculator is not updated merely because the new number appears on the page. The effective date, formula, examples, and user-facing notes must all agree on the same version.
Bringing it all together, if a small business is pricing a new service this week, how would you walk them through a quick checklist that accounts for KDV, payroll load on staffing, potential Damga Vergisi exposure, likely credit costs, and a realistic allowance for Icra Masrafı risk—what’s the one modeling habit that prevents the biggest surprises?
I would start with the amount the business needs to retain after delivering the service, then work backward to the customer price.
- Separate the net service price from KDV so tax collected is never mistaken for revenue.
- Calculate staffing at the full employer cost, including SGK, tax effects, leave, non-billable time and any overtime risk — not only the employee’s net salary.
- Review the contract value, duration and obligations for possible Damga Vergisi exposure before the quotation is signed.
- Add the financing cost created by payment terms. A profitable service can become unprofitable when payroll and suppliers are paid today but the customer pays 60 or 90 days later.
- Include a collection-risk allowance covering delayed payment, follow-up, legal support and possible İcra Masrafı rather than assuming every invoice will be collected fully and on time.
The modeling habit that prevents the biggest surprises is using three cash-flow scenarios instead of one perfect forecast: expected, delayed-payment and problem-collection. I also include a contingency allowance for costs that are difficult to predict at the quotation stage. In finance, I have repeatedly seen an attractive margin disappear because the model assumed that every cost, payment date and collection would proceed exactly as planned.
A price is sustainable only when it still protects cash flow under a realistic weaker scenario — not merely when it shows a profit in the best case.
Thanks for sharing your knowledge and expertise. Is there anything else you'd like to add?
The main point I would add is that a calculator should not create false certainty. A precise result is only useful when the user can also see the assumptions, effective date, formula, source, and costs that may fall outside the calculation.
That is the principle behind HesapCebimde.com. I want small businesses and individuals to test a decision before committing money, compare a normal scenario with a weaker one, and understand which input could change the result the most. In practice, the biggest financial surprises rarely come from difficult mathematics; they come from a tax, fee, delay, or cash-flow gap that was left outside the model.
More information and the calculators are available at https://hesapcebimde.com.