Written by MetricKit EditorialReviewed by MetricKit Editorial ReviewUpdated 2026-05-09
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Pro Rata Investment Calculator
Estimate how much you need to invest in a new round to maintain your ownership percentage (simplified).
Pro rata rights let an existing investor participate in a new round to maintain ownership (subject to terms and allocation).
A simple model can estimate ownership dilution if you do not invest and the investment needed to keep ownership constant.
Prefer an explanation- Read the guide.
Pro rata rights: what they mean and how to estimate your check sizeFundraising & valuation hub: pre/post-money, SAFEs, notes, and liquidation prefsSAFE conversion guide: cap vs discount and dilutionOption pool shuffle: how it impacts founder dilution (with example)
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Tip: you can type commas (e.g., 10,000).
Example
Using the default inputs, the result is:
$250,000.00
- Current ownership
- 5%
- Pre-money valuation
- $20,000,000
- New investment (round size)
- $5,000,000
How to calculate
- Enter your current ownership (before the new round).
- Enter pre-money valuation and new investment amount.
- Review your ownership if you do not participate and your estimated pro rata check size.
Formula
Pro rata check = current ownership % x round size; ownership (no participate) = current % x (pre-money / post-money)
- Simplified model; ignores option pool changes, SAFEs/notes, and share-class terms.
- Assumes ownership is measured on a consistent fully diluted basis before and after the round.
FAQ
Why is pro rata investment current % x round size-
If you own X% and want to keep X% after new shares are issued, you typically need to buy X% of the new issuance, which corresponds to about X% of the round size in a priced round.
Why does ownership drop if I do not participate-
New shares are issued to new investors (and sometimes the option pool), so existing shareholders are diluted unless they buy some of the new shares.
Common mistakes
- Ignoring option pool increases and other dilutive instruments (SAFE/notes).
- Assuming you can always take full pro rata (allocation may be limited).
- Using inconsistent ownership basis (fully diluted vs issued shares).
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Quick checks
- Use consistent time units (monthly vs annual) when entering rates and cash flows.
- Run a sensitivity check on the input that drives the result most (often discount rate or growth).
- Treat the output as a decision aid, not a prediction; validate assumptions with reality.