📜 Bono Return & Discount Calculator

What does the bono calculator compute?

It answers two separate questions. The default “Period Return” mode shows how much a given principal earns at an annual rate over the days left to maturity. The second “Discount Pricing” mode finds today’s purchase price and the effective annual yield of a bono quoted on a face value and a discount rate.

A bono is a debt security that usually matures in under a year and pays a fixed amount at maturity. In Turkey the Treasury’s issues are called Hazine bonosu (Treasury bills), and company issues approved by the Capital Markets Board (SPK) are called finansman bonosu (financing bills). Everyday Turkish calls all of them “bono”, so knowing which type you hold matters, especially for withholding tax (stopaj).

How is period return calculated?

Period return is what the principal earns over the remaining days at the annual rate. With simple interest, gross return = principal × (annual rate ÷ 100) × days ÷ 365, so the annual rate is spread proportionally over the days.

With the compound option the annual rate is read as an effective annual rate, and gross return = principal × ((1 + annual rate ÷ 100) ^ (days ÷ 365) − 1). In both cases the tool also shows the gross return percentage (return ÷ principal) and the gross maturity total (principal + return).

• Principal: the amount you invest or plan to invest; it must be greater than zero.
• Annual interest rate: entered as a percentage (for example 15.5); it may be zero but not negative.
• Days to maturity: a whole number above zero. A year counts as 365 days and the tool sets no 365-day maximum, so 366 days is accepted.

What is the difference between simple and compound interest here?

For the same stated annual rate, simple interest gives a higher return than compound interest on any term shorter than a year, and the two are equal at exactly 365 days. The compound option treats the rate as an effective annual rate and converts it to the shorter period geometrically, while the simple option scales it proportionally.

• 100,000 ₺ at a 40% annual rate for 90 days: simple 9,863.01 ₺; compound 8,650.46 ₺.
• Same amount and rate for 365 days: both give 40,000.00 ₺.
• Same amount and rate for 730 days: simple 80,000.00 ₺; compound 96,000.00 ₺.

Choose the method that matches how the rate is defined in the issue terms or on your broker’s screen. To translate a rate between the two conventions, use the compound-to-simple interest rate converter.

Example: 5,000 ₺, 15.5%, 287 days

Take a principal of 5,000 ₺, an annual rate of 15.5% and 287 days to maturity. These are the values the tool returns for those inputs.

• Simple interest, no withholding selected: gross return 609.38 ₺ (12.19%); gross maturity total 5,609.38 ₺.
• Compound interest, no withholding selected: gross return 599.87 ₺ (12.00%); gross maturity total 5,599.87 ₺.
• Simple + SPK-approved financing bill (15%): withholding 91.41 ₺; net return 517.98 ₺ (10.36%); net maturity total 5,517.98 ₺.
• Simple + other domestic private-sector bond/bill (10%): withholding 60.94 ₺; net return 548.45 ₺ (10.97%); net maturity total 5,548.45 ₺.
• Simple + Treasury bill (0%, if the scope conditions are met): withholding 0.00 ₺; net return equals gross, 609.38 ₺.

Only the withholding choice changes between those lines, yet net return moves between 517.98 ₺ and 609.38 ₺. That gap is why identifying the right category matters.

Gross return, withholding and net return

Gross return is the interest earned before tax. Withholding (stopaj) is income tax deducted at source before the income reaches you. Net return is gross return minus withholding: withholding = gross return × rate; net return = gross return − withholding; net maturity total = principal + net return.

By default the tool shows gross return only. “No withholding selected” does not mean 0%; it means no rate has been chosen and no net figure is calculated. The applicable rate depends on the type of security, its issuer and when it was acquired, and that cannot be inferred reliably from principal, rate and days alone.

What do the withholding options cover?

Each option records how you classify your bono; the tool does not classify it for you. The rates follow the Turkish Revenue Administration’s (GİB) guide on Provisional Article 67 for individual taxpayers.

• Treasury bill (Hazine bonosu) — 0%: income from Treasury-issued government bonds and Treasury bills acquired between 22.12.2021 and 31.12.2026 under the temporary regime. Because the regime is time-limited, do not assume 0% outside that window.
• Other domestic private-sector bond/bill — 10%: the general rate for interest income on domestic private-sector bonds and bills held by individuals. Special-rate instruments and cohorts are excluded.
• SPK-approved financing bill (finansman bonosu) — 15%: the rate set by Presidential Decision 2569 for financing bills approved under Law 6362. It applies to acquisitions on or after 24.05.2020, the Decision’s publication date; earlier acquisitions are taxed at 10%.
• Custom rate — I will enter it: for cases outside these scopes or when you know the rate from another source. Any value from 0 to 100 is accepted, and the tool does not verify that it applies to you.

The presets do not cover the reduced rates applied to bank-issued bonds acquired between 23.12.2020 and 31.01.2025, securities issued before 2006, or the different rules for investors that are not individuals. Use the custom rate or the gross figure in those cases.

When to use Discount Pricing mode

Discount Pricing finds today’s purchase price of a bono that pays its face value at maturity and is quoted at a discount rate. Purchase price = face value × (1 − discount rate ÷ 100 × days ÷ basis), and you can choose a 365-day or 360-day basis.

For example, a bono with a 100,000 ₺ face value, a 45% annual discount rate and 120 days to maturity has a purchase price of 85,205.48 ₺, a total return of 14,794.52 ₺ and an effective annual yield of 52.81% on the amount paid. The effective yield is higher than the discount rate because the discount is figured on the face value while you pay the lower price.

This mode does not calculate withholding. For a business discounting a trade note, see the inner and outer discount calculator; for coupon-paying bonds, see the bond price calculator.

Common mistakes

• Confusing a discount rate with an interest rate: a discount is figured on face value, interest on principal, and the two modes answer different questions.
• Applying 15% withholding to every bono: the rate depends on the category and acquisition date.
• Reading the default result as net: with no withholding selected, the figure is gross.
• Comparing a gross return with a net one: compare investments on the same basis.
• Typing the rate as a fraction such as 0.155: the tool expects a percentage like 15.5.
• Forgetting commissions, fees and price rounding, which can change the figure you actually get from a broker.

What the tool does not calculate

• It shows no live or current market price, rate or yield; you enter the rate.
• It does not decide which withholding category your bono belongs to; the selection is your own classification.
• It does not cover coupon-paying bonds, issuer-specific terms, commissions or brokerage fees.
• It is not tax advice; for filing obligations and your personal tax position, consult official sources or a professional.