Convertible Debt Calculator

The Convertible Debt Calculator estimates conversion outcomes, interest accrual, dilution, and valuation cap and discount impacts across rounds.

About the Convertible Debt Calculator

The Calculator estimates how a convertible note converts into shares at a priced round or another trigger event. It computes accrued interest, the conversion price using a discount and/or valuation cap, and the resulting share count. It also estimates post-financing ownership using a simple, transparent capitalization model.

Real-world deals vary. Notes can use simple interest or compounding. Caps can be pre-money or post-money, and capitalization definitions differ. Our approach spells out the assumptions and the inputs so you can test ranges and compare outcomes. The result is a practical tool to sanity-check term sheets and to prepare for negotiations.

How the Convertible Debt Method Works

Convertible debt is a loan that turns into equity, usually preferred stock, when a qualified financing occurs. Until it converts, it accrues interest. At conversion, a price per share is calculated, often using the lower of a discount to the round price or a price implied by a valuation cap.

• Accrue interest on the principal from the issue date until the conversion date.
• Find the round price per share based on the new financing valuation and the capitalization definition in the note.
• Compute a discounted price (round price multiplied by 1 minus the discount rate).
• Compute a cap price (valuation cap divided by the defined fully diluted share count). Choose the lower of discounted or cap price.
• Divide accrued principal plus accrued interest by the chosen conversion price to get the number of shares issued to the noteholder.
• Recalculate ownership using the updated fully diluted cap table after the financing, including the new preferred shares and converted notes.

Some notes convert at maturity if no financing occurs, often at a negotiated price or a fixed cap. Others may be repaid. The Calculator assumes a financing-based conversion by default but allows alternative triggers in the inputs.

Equations Used by the Convertible Debt Calculator

These equations describe the core steps. Variables: P0 = principal, r = annual interest rate, m = compounding periods per year, t = years outstanding, D = discount rate, Vpre = pre-money valuation, FDpre = fully diluted pre-money shares, Cap = valuation cap, Pround = round price per share, Pdisc = discounted price, Pcap = cap price, Pconv = conversion price, A = accrued amount (principal + interest), Snote = shares issued to note.

• Accrued amount with compounding: A = P0 × (1 + r/m)^(m × t). With simple interest: A = P0 × (1 + r × t).
• Round price per share (pre-money basis): Pround = Vpre ÷ FDpre. If a post-money basis is used, adjust the denominator per the note’s definition.
• Discounted price: Pdisc = Pround × (1 − D).
• Cap price (pre-money cap): Pcap = Cap ÷ FDpre. Some notes define FDpre to exclude or include different pools; the definition controls.
• Conversion price: Pconv = min(Pdisc, Pcap) if both apply; otherwise use whichever applies.
• Shares from the note: Snote = A ÷ Pconv.

Where multiple notes convert, compute each accrued amount and share count, then total them for the post-financing denominator. For precision, the Calculator carries more decimals during the computation, then rounds share counts to the nearest whole share.

Inputs, Assumptions & Parameters

To run the analysis, the Calculator needs a small set of inputs. Each input ties directly to a term in the note or to the priced round. If a term is missing, you can use a reasonable estimate and test a few scenarios to see the outcome ranges.

• Principal amount: The original face value of the note.
• Annual interest rate and method: Simple or compounded (choose m, such as monthly or annual).
• Discount rate: Percentage deduction applied to the round price per share.
• Valuation cap and basis: The cap value and whether the definition uses pre-money or post-money shares.
• Round price basis and capitalization: Pre-money valuation and fully diluted share count used to compute the round price.
• Conversion trigger date: The date used to measure time outstanding (t) and to accrue interest until conversion.

Notes can include extra features like MFN, warrants, or conversion at maturity without a financing. Those are optional parameters. Edge cases include caps defined on a post-money basis, super pro-rata allocations, or carve-outs from fully diluted shares. The Calculator flags unusual inputs and suggests ranges when values look out of step with market norms.

Step-by-Step: Use the Convertible Debt Calculator

Here’s a concise overview before we dive into the key points:

1. Enter the note’s principal and the issue date.
2. Select the annual interest rate, and choose simple or compounding with the compounding frequency.
3. Enter the discount rate and the valuation cap, and pick the cap basis (pre-money or post-money).
4. Enter the priced round’s pre-money valuation and the fully diluted pre-money share count.
5. Set the conversion date, which determines the time outstanding for interest accrual.
6. Optionally add other notes, warrants, or an option pool increase, if relevant to the cap table.

These points provide quick orientation—use them alongside the full explanations in this page.

Real-World Examples

A seed note has $250,000 principal, 6% simple interest, a 20% discount, and a $6,000,000 valuation cap. It converts 18 months later into a Series A at a $10,000,000 pre-money valuation with 10,000,000 fully diluted pre-money shares. The round price per share is $1.00. The discounted price is $0.80. The cap price is $6,000,000 ÷ 10,000,000 = $0.60. Interest accrues to $250,000 × (1 + 0.06 × 1.5) = $272,500. The note takes the lower price, $0.60, so it converts into 272,500 ÷ 0.60 = 454,167 shares. If the company sells 5,000,000 Series A shares for cash, post-financing shares are 10,000,000 + 5,000,000 + 454,167 = 15,454,167, and the noteholder owns about 2.94%. What this means

A bridge note has $500,000 principal, 8% annual compounding, a 25% discount, and no cap. Twelve months later, a priced round occurs at an $8,000,000 pre-money valuation with 8,000,000 fully diluted pre-money shares, so the round price is $1.00. Accrued amount is $500,000 × (1 + 0.08) = $540,000. The discounted price is $0.75, and there is no cap. Shares issued are $540,000 ÷ $0.75 = 720,000. If the round sells 4,000,000 shares for cash, the total after financing is 8,000,000 + 4,000,000 + 720,000 = 12,720,000 shares. The noteholder owns about 5.66%. What this means

Assumptions, Caveats & Edge Cases

The Calculator follows common market conventions but your documents control. Read the note’s definitions. Different capitalization definitions can shift the conversion price and the resulting ownership. You can test multiple scenarios by toggling inputs and comparing the breakdown.

• Cap basis matters: Pre-money vs post-money caps lead to different cap prices and share counts.
• Interest method matters: Simple vs compounding changes the accrued amount and therefore the shares issued.
• Qualified financing triggers: If the round does not meet the threshold, the note may not convert yet.
• Multiple notes: Convert each note under its terms, then include all note shares in the denominator for ownership.
• Option pool top-ups: If the round increases the option pool pre-money, those shares often count in FDpre.

If your note includes MFN, warrants, or special conversion mechanics, enter those as additional assumptions. When uncertain, run a few ranges to see best-case and worst-case outcomes and discuss them with counsel.

Units & Conversions

Convertible debt math uses currency, percentages, time, and share counts. Misreading units leads to errors. For example, entering 8 instead of 8% produces a massive overstatement. This quick guide shows common units and how to convert them for inputs.

When entering percentages, watch the format the Calculator expects. If it asks for a decimal, enter 0.20 for a 20% discount. If it asks for a percent, enter 20. Time can be in months or years; the tool converts ranges consistently.

Tips If Results Look Off

If your output seems unrealistic, the issue is often an input mismatch. Many errors come from confusing discounts, caps, or capitalization definitions. Walk back through the inputs and check each definition against the note.

• Confirm whether the cap is pre-money or post-money and whether FDpre includes the option pool top-up.
• Verify interest method and compounding frequency.
• Ensure the discount is a percent, not a decimal, or vice versa, as required.
• Check the round’s share price math: valuation divided by fully diluted shares.
• If multiple notes exist, include every note’s accrued amount and shares in the totals.

Still stuck? Try bracketing the result with low and high ranges. Then compare the breakdown line by line to your term sheet.

FAQ about Convertible Debt Calculator

What is the difference between a discount and a valuation cap?

A discount reduces the round price by a fixed percentage. A valuation cap sets an upper bound on the company valuation used to compute the conversion price. The note converts at the lower resulting price.

Does the Calculator handle simple and compound interest?

Yes. You choose simple interest or compounding, and you select the compounding frequency. The Calculator then accrues interest until the conversion date.

How does a post-money cap change the result?

A post-money cap often assumes more shares in the denominator, which can raise the cap price and reduce note shares. The Calculator lets you select the basis and the capitalization definition used.

Can I include multiple notes and an option pool increase?

Yes. You can enter several notes and an option pool top-up. The tool sums all converted note shares and pool shares before computing final ownership.

Key Terms in Convertible Debt

Convertible note

A short-term loan to a company that converts into equity, usually at a future priced financing, instead of being repaid in cash.

Valuation cap

A contractual maximum valuation used to set the conversion price, protecting early investors if the next round’s valuation is high.

Discount rate

A percentage reduction from the priced round’s share price, rewarding early investors with a lower conversion price.

Maturity date

The date when the note comes due. If no financing occurs by then, the note may convert at a set price or be repaid, depending on the terms.

Qualified financing

A priced equity financing that meets a minimum size threshold, which triggers automatic conversion of the note.

Most favored nation (MFN)

A clause giving the noteholder the right to adopt better terms offered to later investors in similar instruments.

Fully diluted capitalization

The total shares outstanding assuming all options, warrants, and convertibles are exercised or converted, as defined in the note.

Conversion price

The price per share at which the note converts into equity, usually the lower of the discounted round price or the cap price.

Disclaimer: This tool is for educational estimates. Consider professional advice for decisions.

References

Here’s a concise overview before we dive into the key points:

• Cooley GO: Convertible Notes in Seed Financing
• Y Combinator: SAFE Financing Documents and Guides
• Startup Company Lawyer: What Is a Valuation Cap?
• Investopedia: Convertible Note Definition
• Brad Feld: Term Sheet – Convertible Debt

These points provide quick orientation—use them alongside the full explanations in this page.