FinToolSuite

Convertible Bond Calculator

Updated April 17, 2026 · Investing · Educational use only ·

Compare a convertible bond's value as a bond vs converted to shares.

Work out whether a convertible bond is worth more as a bond or converted into shares. Enter face value, conversion ratio and share price.

What this tool does

A convertible bond can be held to maturity for its face value or exchanged into a fixed number of shares at the bondholder's choice. Enter the face value, the conversion ratio (shares per bond), and the current share price. The tool returns the higher of the two values, the conversion premium or discount, and flags whether conversion is currently profitable.


Enter Values

Formula Used
Bond face value
Conversion ratio
Current share price

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Disclaimer

Results are estimates for educational purposes only. They do not constitute financial advice. Consult a qualified professional before making financial decisions.

A bond with a 1,000 face value converting into 20 shares at a 60 share price has a conversion value of 1,200 — worth more converted than held. A share price of 45 gives a conversion value of 900, so the bond is worth more as debt.

How to use it

Enter the bond's face value (or its current market price if you're comparing a traded convertible), the conversion ratio (how many shares each bond converts into), and the share price.

What the result means

The primary result is the higher of bond value and conversion value — the minimum rational bondholder value today. The secondary rows show both sides and the gap. A positive conversion premium means the bond is trading above its conversion value (common while the option has time value); a negative one means the bond is trading at a discount to its convert-and-sell value.

What this doesn't model

Time value, credit risk, call features, and coupon cash flows. For a full convertible valuation you need a binomial tree or Monte Carlo approach. This tool gives you the floor — the higher of the two simple values — which is usually the useful first check.

A worked example

Try the defaults: bond face value of 1,000, conversion ratio of 20, current share price of 60. The tool returns 1,200.00. You can adjust any input and the result updates as you type — no submit button, no reload. That's the real power here: seeing how sensitive the output is to one or two assumptions.

What moves the number most

The result responds to Bond Face Value, Conversion Ratio, and Current Share Price. Not every input has equal weight. Flip one at a time toward extreme values to feel which ones move the needle most for your situation.

The formula behind this

The rational holder value is the higher of the bond's face value and its conversion value (ratio × share price). This is a simplified view — it ignores coupon value, time to maturity, credit spread, call features, and option time value. For a traded convertible, market price typically sits above this floor. Everything the calculator does is shown in the formula box below, so you can check the math against your own spreadsheet if you want.

Using this well

Treat the output as one point on a wider map. Run it three times — a pessimistic case, a central case, and a stretch case — and plan against the pessimistic one. That habit alone separates people who stick with an investment plan from those who bail at the first wobble.

What this doesn't capture

Steady-rate math ignores real-world volatility. Actual returns are lumpy; sequence-of-returns risk matters most in drawdown; fees and taxes drag on compound growth; and behaviour changes in drawdowns can reduce outcomes below the projection. Treat the number as one scenario, not a forecast.

Example Scenario

The higher of bond value and conversion value at your inputs is shown above.

Inputs

Bond Face Value:1,000 £
Conversion Ratio:20
Current Share Price:60 £
Expected Result£1,200.00

This example uses typical values for illustration. Adjust the inputs above to match a specific situation and see how the result changes.

Sources & Methodology

Methodology

The rational holder value is the higher of the bond's face value and its conversion value (ratio × share price). This is a simplified view — it ignores coupon value, time to maturity, credit spread, call features, and option time value. For a traded convertible, market price typically sits above this floor.

Frequently Asked Questions

What is the conversion premium?
The conversion premium is how much more (or less) the bond's price is vs its conversion value. A positive premium reflects the option time value — the chance the share price rises further before maturity.
Should I always convert when the share value is higher?
Not always. If the bond still pays coupons and there's time to maturity, you often keep the option value by holding rather than converting early. Most convertibles are converted just before call or expiry.
Does this include coupons?
No. Coupon cash flows are additional value on top. If the bond pays a 3% coupon for 5 more years, add roughly 15% of face to the bond side when comparing.
What's a typical conversion ratio?
Set at issue so the conversion price is 20-40% above the then-current share price. Once shares rise to the conversion price, the bond starts trading in line with the underlying.

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