The conversion parity price of a convertible bond is the stock price at which converting the bond would exactly break even against what the bond currently costs on the market. You calculate it by dividing the bond’s market price by its conversion ratio. If the underlying stock trades above that number, converting puts you ahead; if it trades below, the conversion feature is underwater. The figure moves constantly, because the bond’s market price moves constantly.
The Formula and a Worked Example
Conversion Parity Price = Bond Market Price ÷ Conversion Ratio.
You need two inputs. The conversion ratio comes from the bond’s indenture or prospectus and tells you how many shares you receive for each bond surrendered. Tesla’s 2017 convertible note offering, for example, specified a conversion rate of 3.0534 shares per $1,000 of principal, which worked out to a conversion price of roughly $327.50 per share at issuance.1U.S. Securities and Exchange Commission. Tesla, Inc. Prospectus Supplement – Section: Description of Notes – Conversion Rights The second input is the bond’s current market price, which is whatever it trades for on its exchange and often differs from its $1,000 par value.
Suppose a convertible bond trades at $1,200 and its conversion ratio is 40 shares. Dividing $1,200 by 40 gives a conversion parity price of $30. If the stock trades at $30, converting produces shares worth exactly what you paid for the bond. At $35, you come out ahead by converting. At $25, converting destroys value.
You can run the math from the other side to double-check. Multiply the conversion ratio by the current stock price and you get the bond’s conversion value. With 40 shares and a $35 stock, that’s $1,400. Compare that to the bond’s $1,200 market price and the story is the same one the parity price tells, just read in the opposite direction.
Conversion Price Is Not the Conversion Parity Price
These two numbers get confused constantly, and the difference is the whole point of the parity calculation.
The conversion price is fixed when the bond is issued. It equals par value divided by the conversion ratio. A $1,000 par bond with a conversion ratio of 40 shares has a conversion price of $25, and that number stays put for the life of the bond unless a corporate action adjusts it.
The conversion parity price moves every time the bond’s market price moves. It answers a different question: given what the bond trades for right now, what stock price would make conversion a wash? A bond trading at $1,200 with a ratio of 40 has a parity price of $30 today. If it drops to $1,100 tomorrow, the parity price drops to $27.50. The conversion price is what the issuer originally set as the exchange rate. The parity price is what the market currently implies.
What the Number Tells You
Compare the parity price to the stock’s actual market price and you get one of three readings.
- At parity. Stock price equals parity price. Converting gives you shares worth exactly the bond’s market value. This is the theoretical break-even.
- Above parity. Stock price exceeds parity price. The shares from conversion are worth more than the bond costs, so the conversion feature is in the money.
- Below parity. Stock price sits below parity price. Converting would hand you shares worth less than the bond, so the feature is out of the money.
Most convertible bonds trade below parity for most of their lives. The bond costs more than the raw conversion value of the shares because it also pays interest and returns your principal at maturity. Those features have value that pure stock ownership doesn’t. When the stock drops sharply, the bond’s price finds a floor near its value as a straight debt instrument and loses sensitivity to the stock entirely. When the stock climbs well above the conversion price, the bond starts tracking the stock almost one-to-one, because the conversion feature dominates everything else.
The Conversion Premium
Parity price has a companion number: the conversion premium, which measures how much extra you pay for the bond versus the shares it converts into.
Conversion Premium (%) = [(Bond Market Price − Conversion Value) ÷ Conversion Value] × 100.
If a bond trades at $1,200 and its conversion value is $1,000 (40 shares at a $25 stock price), the premium is 20%. You’re paying 20% more than the shares are worth for a security that also pays interest and protects your principal on the downside.
Premiums shrink as the stock rises well above the conversion price, because the bond’s value becomes almost entirely driven by the conversion feature. Premiums expand when the stock falls near or below the conversion price, because at that point the bond is essentially a straight bond with a long-shot option attached. Reading the premium alongside the parity price gives you a fuller picture of whether a convertible is cheap or expensive relative to its equity upside.
Why the Conversion Ratio Can Change
The parity formula depends on the conversion ratio, and the ratio is not always permanent. Anti-dilution provisions in the indenture protect investors from corporate actions that would otherwise erode the conversion feature. A 2-for-1 stock split halves the share price and doubles the ratio: a bond that converted into 40 shares before the split converts into 80 after, keeping the economic relationship intact.
Similar adjustments apply to large stock dividends, rights offerings, and spin-offs. Tesla’s 2017 prospectus specified that the conversion rate would be adjusted for certain events but would not change for accrued and unpaid interest.1U.S. Securities and Exchange Commission. Tesla, Inc. Prospectus Supplement – Section: Description of Notes – Conversion Rights Not every event triggers an adjustment. Ordinary cash dividends and small stock dividends below a threshold set in the indenture typically leave the ratio alone. The prospectus spells out exactly which events qualify, so if you’re running parity math around a corporate event, read the actual document rather than relying on general rules.
Where Parity Stops Telling You the Whole Story
Parity is a market comparison tool. A few things it does not account for are worth knowing before you act on it.
Forced Conversion Caps Your Upside
Many convertible bonds include a soft call provision that lets the company force conversion once the stock trades above a threshold for a specified period. A common structure requires the stock to trade at or above 130% of the conversion price for 20 out of 30 consecutive trading days before the issuer can call. When that trigger hits, the company redeems the bonds at par plus accrued interest, and bondholders almost always convert instead because the shares are worth more than the redemption price. Most convertibles also carry hard call protection, often three to five years after issuance, during which the issuer cannot call regardless of the stock price. Once that window closes, a rising stock may force your hand well before you planned to convert.
Many modern convertibles are also contingently convertible, meaning you can only convert when certain conditions are met, typically the stock trading at around 130% of the conversion price for a minimum period. Outside those windows, you can’t convert even if parity says you should.
Accrued Interest and Fractional Shares
Two costs catch investors off guard between coupon dates. Many convertible bonds state that accrued but unpaid interest is forfeited upon conversion. Convert three months after the last coupon and you lose three months of interest. Not every bond works this way, but the forfeiture clause is common enough to check before converting mid-period. Timing a conversion just after a coupon payment minimizes the hit.
Conversion ratios also rarely produce whole shares. A ratio of 3.0534 per $1,000 bond leaves a fractional share. Indentures usually pay cash for the fractional portion based on the stock’s current market price, though some round to the nearest whole share. Cash received for a fraction is typically taxable even though the conversion itself is not.
Parity Price Is Not Your Cost Basis
Converting a bond into stock of the same issuer is generally not a taxable event. Federal tax law provides that no gain or loss is recognized when securities in a corporation are exchanged solely for other securities in that corporation as part of a qualifying exchange.2Office of the Law Revision Counsel. 26 U.S. Code 354 – Exchanges of Stock and Securities in Certain Reorganizations Your basis in the bond carries over to the new shares.3Office of the Law Revision Counsel. 26 U.S. Code 358 – Basis to Distributees
If you bought a bond for $950 and later convert into 40 shares, your cost basis per share is $23.75, not whatever the parity price was on the conversion date. Parity is a market signal; cost basis is a tax number tied to what you actually paid. You recognize no gain or loss until you sell the shares. One exception: converting into stock of a different company, as can happen in a merger, is taxable, and any cash received alongside shares may trigger gain recognition on its own.