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Anti-dilution Calculator: Broad-based, Narrow-based & Full Ratchet

Raising a down round? See how anti-dilution protection reprices earlier investors. Enter the original price, the new lower price and share counts to get the adjusted conversion price, extra shares and the ownership hit to founders.

QUICK ANSWERAnti-dilution protection lowers an investor’s conversion price if the company later issues shares at a lower price. Broad-based weighted average (the market norm) uses CP2 = CP1 × (A + B) ÷ (A + C). Full ratchet resets the price all the way to the new price and is very founder-unfriendly.

CP2 = CP1 × (A + B) ÷ (A + C)
A = shares outstanding before the issue (all fully diluted for broad-based)
B = new money ÷ CP1     C = new shares actually issued
Full ratchet: CP2 = new issue price

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⚠️ Illustrative only. Not legal advice.

What the Anti-dilution Calculator does

✅ Broad-based and narrow-based weighted average
✅ Full ratchet
✅ Adjusted price and extra shares
✅ Ownership before and after
✅ Formula shown with your numbers

How to use the Anti-dilution Calculator

STEP 1
Enter your numbers
Type the figures you know. Every field starts with a realistic example so you can see how it works.
STEP 2
Read the result instantly
Results, tables and the plain-English explanation update as you type. No submit button, no login.
STEP 3
Test scenarios
Change one assumption at a time (valuation, growth, dilution, exit) to see what really moves the outcome.
STEP 4
Share or save
Copy the summary, send it on WhatsApp or print to PDF for your co-founders, board or investment committee.

Weighted average vs full ratchet

Weighted average adjusts the price in proportion to how many cheap shares are issued: a small down round produces a small adjustment. Broad-based counts all fully diluted shares in A, making the adjustment smaller than narrow-based, which counts only some classes.

Full ratchet ignores size: one share issued at a lower price reprices the whole protected round. The extra shares come out of founders, employees and unprotected investors, which is why founders should push back hard on full ratchet.

Worked example

Series A at ₹1,000 per share; a down round issues 2.5 L shares at ₹600 on 10 L fully diluted shares. Broad-based weighted average adjusts the price to ₹920; full ratchet to ₹600. On 2 L protected shares that is about 17,400 vs 1,33,300 extra shares.

Frequently asked questions

What is broad-based weighted average anti-dilution?

A formula that reduces the protected investor’s conversion price based on how much new money came in at a lower price relative to all fully diluted shares. It is the standard in Indian and US venture deals.

Who pays for anti-dilution adjustments?

Everyone who is not protected, mainly founders, employees with ESOPs and investors without anti-dilution rights, because the protected investor receives extra shares.

Are there exceptions to anti-dilution?

Yes. Typical carve-outs include ESOP grants within the approved pool, shares on conversion of existing securities, and issues approved by the investors.

Is this tool free? Do I need to sign up?

Yes. It is completely free, needs no login and has no usage limit. FastFee builds payment collection software; these startup and investor tools are free resources for founders, angels and fund managers.

Is my data private?

Yes. Everything you type stays in your own browser on this device (local storage). Nothing is uploaded to FastFee. Export or print a copy if you need to keep it.

Use it together with

Liquidation Preference Calculator →Exit waterfall for multiple preferred series: who gets what at any sale value.Term Sheet Comparator →Compare two term sheets on effective valuation, dilution, preferences and founder payout at exit.

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