📈 Bond Return & Coupon Price Calculator

What does this bond calculator compute?

The tool answers two different questions. The default “Period Return” mode computes how much a given principal earns at an annual rate over the remaining days. The “Theoretical Coupon Price” mode finds what a coupon bond should be worth today for the yield you expect.

In Turkey a bond (tahvil) is usually a debt security issued by the state or a company with a maturity of more than one year; a bono is its shorter-term counterpart. Period return mode uses the same arithmetic for either when you know the days left and an annual rate, but it does not model coupon dates, trading prices or payment calendars.

How is period return calculated?

Period return is the amount your principal earns over the days remaining at the annual rate. For simple interest, gross return = principal × (annual rate ÷ 100) × days ÷ 365. For compound interest, gross return = principal × ((1 + annual rate ÷ 100) ^ (days ÷ 365) − 1); the rate you enter is the effective annual rate reached after one year (365 days).

• Principal: the amount you invest or plan to invest; it must be above zero and no finer than cents (two decimals).
• Annual interest rate: written as a percentage (for example 15.5). It can be zero but not negative.
• Interest type: Simple (default) or Compound.
• Days to maturity: a whole number from 1 to 36,500. A year counts as 365 days; day 366 can also be entered.

The result shows the gross return as an amount and as a share of the principal. That percentage is the total return of your chosen period, not an annual figure. Amounts are rounded to cents and the totals are built so the screen adds up: the displayed gross return minus the displayed withholding equals the displayed net return.

What is the difference between simple and compound interest?

With simple interest, return grows in direct proportion to the days: 730 days earns twice the return of 365 days. With compound interest, earned return is added to the principal and earns interest as well, so the gap widens as the term gets longer.

For example, a principal of 5,000 ₺ at 15.5% a year over 365 days gives 775.00 ₺ with either method. Over 730 days simple interest gives 1,550.00 ₺ and compound interest 1,670.13 ₺. Over short periods the gap is small: 30 days gives 63.70 ₺ simple and 59.57 ₺ compound, because the compound method converts the effective annual rate into an equivalent rate for the number of days.

When is withholding tax (stopaj) included?

By default no withholding is calculated and only the gross return is shown. That does not mean the withholding is 0%. The rate depends on the instrument type, the issuer and the date you acquired the bond, so the tool never guesses it for you.

If you choose a category that fits you and tick that you are calculating as an individual, the tool applies an estimated withholding to the gross return according to the verified groups below. If you do not tick it, no official rate is applied. When conditions are missing, uncertain or outside a group, the gross return is shown again.

• Devlet tahvili and Hazine bonosu issued by the Treasury and Finance Ministry: 0% if acquired from 22.12.2021 to 31.12.2026; 10% if acquired from 1.1.2006 to 21.12.2021. For acquisitions from 1.1.2027 the rate depends on the decision in force, so only the gross return is shown.
• Domestic private-sector bonds and bills (financing bills excluded): 10%. For bank-issued bonds acquired before 1.2.2025, reduced maturity-based rates may have applied, so the gross return is shown instead.
• SPK-approved financing bills (finansman bonosu): 15% if acquired on or after 24.5.2020.

If your instrument is not on the list or you want a different assumption, choose “I'll enter my own rate” and type a rate from 0 to 100. That rate is your own assumption; the tool does not verify that it applies legally and only applies it arithmetically.

What is the theoretical coupon price mode for?

The theoretical price of a coupon bond is the sum of its future coupon payments and its face value at maturity, discounted to today at the yield you expect. If your expected yield is above the coupon rate, the theoretical price is below face value; if it is lower, the price is above face value.

In this mode you enter the face value, the annual coupon rate, the expected annual yield, the number of coupon payments per year (1, 2 or 4) and the number of coupon payments remaining. It asks for coupon counts rather than years because bond pricing is only defined on discrete coupon dates and a fractional year would force a silent rounding.

Example: for a bond with a face value of 100,000 ₺, a 30% annual coupon paid twice a year, each coupon is 15,000 ₺. With a 35% expected annual yield and 4 coupon payments (2 years) remaining, the theoretical price is 93,208.92 ₺.

Worked examples

1. 5,000 ₺, 15.5% a year, 365 days, simple interest: gross return 775.00 ₺, gross total 5,775.00 ₺.
2. In the same calculation, if you select a Treasury bond acquired in 2024, withholding is 0.00 ₺ and net return is 775.00 ₺. If acquired in 2020, withholding at 10% is 77.50 ₺, net return 697.50 ₺ and net total 5,697.50 ₺.
3. In the same calculation, entering 12.5% as your own rate shows withholding of 96.88 ₺, net return 678.12 ₺ and net total 5,678.12 ₺.
4. 5,000 ₺ at 15.5% a year for 30 days: gross return 63.70 ₺ with simple interest, 59.57 ₺ with compound.

Common mistakes

• Treating the annual rate as a period rate: the tool asks for an annual rate and divides the days by 365 itself.
• Mixing up the coupon rate and the expected yield: the coupon is what the bond pays, while the expected yield is your market assumption.
• Reading “Not sure” or the default choice as 0% withholding: in both cases no withholding is calculated and only the gross return is shown.
• Confusing the acquisition date with the maturity date: for a Treasury bond the rate depends on when you acquired it, not when it matures.
• Reading period return as the bond's purchase price: period return is the gain on your principal; the theoretical price is a separate mode.

Limits and cautions

The tool shows the arithmetic return of your principal at the rate you enter. It does not model coupon dates, trading prices, commissions, accrued interest, issuer risk or the actual payment day. The withholding calculation covers only the stated groups of individual investors and is an estimate; it is not a substitute for tax advice.

How it differs from similar calculators

For short-term and discounted debt securities, the Bono Return & Discount Calculator also gives the purchase price and yield of instruments maturing in under a year. Discounting a commercial note at a bank is the subject of the Bill Discount Calculator. A repo is short-term borrowing against a security under a buy-back agreement and is calculated separately with the Repo Calculator. To see how compound and simple rates convert into each other, use the Compound to Simple Interest Rate Converter.