Stacked SAFEs: How Multiple SAFE Notes Convert at Your Series A

You raised $250,000 on a SAFE with a $10 million cap, then $500,000 at a $12 million cap, and later $1 million at a $15 million cap. Now you are closing a Series A at a $25 million pre-money valuation. The founder ownership number depends on the exact SAFE versions, discounts, side letters, fully diluted capitalization, and option-pool terms. A spreadsheet that omits any of those inputs can be materially wrong, but the size of the error is deal-specific.

Stacked SAFE conversion is therefore a document-and-data problem, not a fixed dilution shortcut. This article explains the standard concepts, shows conditional calculations, and identifies the inputs to reconcile before relying on a Series A model.

Below: how stacked SAFE conversion works, where spreadsheet assumptions can break, and when a deal-specific waterfall helps you negotiate from a defensible number.

What Is a Stacked SAFE Situation?

For this article, a stacked SAFE situation means multiple outstanding SAFEs that may convert in the same Equity Financing. The modeling difficulty depends on the signed terms and capitalization data, not on a universal SAFE count.

Review each instrument's form, valuation cap or discount, MFN language, optional pro rata side letter, and Company Capitalization definition. Different versions can produce different results, and a cap-table system does not necessarily flatten those differences. The signed documents remain the controlling source.

How Does Stacked SAFE Conversion Work at a Priced Round?

A SAFE generally converts using the method that gives the holder more shares: the applicable valuation-cap price or the applicable discount to the priced-round price. The cap price is calculated using the SAFE's defined Company Capitalization, not an arbitrary denominator. A valuation cap is a pricing ceiling for the conversion calculation, not a statement that the company was finally valued at that amount. See the current YC SAFE financing documents and SAFE User Guide for the standard form framework.

For a single SAFE at a 10 million dollar cap converting in a 25 million pre-money Series A:

• Cap-based price relative to the priced-round price: 10M / 25M = 40%, if the same denominator is used for this illustration
• Illustrative effective price reduction: 60%
• Actual share counts: determined by the SAFE's Company Capitalization and the financing documents

That 60% figure is an illustrative effective price reduction, not a universal conversion result. The complication starts when multiple instruments use different definitions, versions, or side letters.

What Changes With Multiple Valuation Caps?

When multiple standard post-money SAFEs convert in one Equity Financing, each uses its applicable terms and the signed form's Company Capitalization definition; that is not a founder-selected legal sequence. Because converting securities can be included without double counting, the calculation can be circular and may require an equation or iteration.

A worked example with three SAFEs (all post-money, no discount, no MFN):

• SAFE 1: 250K invested at a 10M cap
• SAFE 2: 500K invested at a 12M cap
• SAFE 3: 1M invested at a 15M cap

Assume three standard post-money valuation-cap SAFEs, no discounts, no MFN rights, and no priced-round pool increase. Their stated cap percentages are 250,000 / 10,000,000 = 2.500%, 500,000 / 12,000,000 = 4.167%, and 1,000,000 / 15,000,000 = 6.667%. Together they represent 13.333% of the pre-Series A Company Capitalization under this simplifying model. They are not produced by a legal sequence in which one SAFE changes the next SAFE's terms.

An $8M Series A at a $25M pre-money valuation represents 8 / (25 + 8) = 24.242% of the post-money company under the simple valuation model. Existing pre-money holders, including the SAFE shares, are diluted by the Series A. The three SAFE holders therefore represent approximately 13.333% x 25 / 33 = 10.101% after the Series A, before any option-pool or other term-sheet adjustment.

The total math is not a universal 13.4% answer. It is 13.333% before the priced round under the assumptions above, and approximately 10.101% after that Series A before other adjustments. A different SAFE version, capitalization definition, discount, pool refresh, or side letter changes the result.

Post-Money vs Pre-Money SAFEs: Why the Difference Matters

YC introduced the post-money SAFE in 2018. In the standard post-money form, the cap is measured after the SAFE financing is accounted for, including converting securities included in Company Capitalization, but before the new money in the priced round. Later post-money SAFEs do not dilute an earlier post-money SAFE in the way they dilute a pre-money SAFE, but the priced-round shares do dilute the earlier SAFE.

Practically, a company that raised an early pre-money SAFE and later post-money SAFEs may hold a mix of treatments. The effect depends on the operative definitions and any side letters, not only on the label used in a spreadsheet.

Two questions to answer before any Series A modeling:

• Which version of the SAFE template did each round use, and what do its Company Capitalization definitions include?
• Do the documents include discounts, MFN language, promised options, or optional pro rata rights?

Check the signed document. A post-money form generally identifies a "Post-Money Valuation Cap" and includes converting securities in Company Capitalization. A pre-money form generally uses a pre-money cap and excludes other SAFEs from that definition. The title alone is not a substitute for reading the operative definitions and side letters.

How Do MFN Clauses Compound the Dilution?

An MFN provision can give an early SAFE holder a right to elect the terms of a later SAFE, but the result depends on the exact MFN language, timing, exclusions, and the holder's election. Do not assume the holder can mix and match the lowest cap, largest discount, and other isolated terms from different SAFEs.

The current YC US documents page lists an uncapped MFN post-money form as a separate form from valuation-cap-only and discount-only forms. A SAFE that appears to combine a cap, discount, and MFN requires the actual customized document or side letter. Compare the elected instrument's actual conversion economics at the modeled priced-round valuation. For example, at a $25M priced-round valuation, a $10M cap is 40% of the round price, while a $12M cap with a 15% discount is 40.8%; the original $10M cap is slightly better in that comparison. A $15M cap is better than a $15M cap with a 20% discount in the same scenario.

What Does Stacked SAFE Dilution Actually Look Like? (Worked Example)

The cleanest way to see stacked SAFE math is to state every assumption and calculate one conditional waterfall; the result is not a universal answer for every Series A.

Assume a company entering a Series A with:

• 10M founder common shares outstanding
• 2M shares in the existing option pool (16.667% of the stated 12M pre-financing shares)
• SAFE 1: 250K at a 10M post-money cap, with MFN
• SAFE 2: 500K at a 12M post-money cap
• SAFE 3: 750K at a 12M post-money cap, 15% discount
• SAFE 4: 1M at a 15M post-money cap, 20% discount
• SAFE 5: 1.5M at a 15M post-money cap, MFN
• Series A: 8M at 25M pre-money, with a top-up to 12% post-money option pool

Under explicit assumptions, treat all five instruments as standard post-money valuation-cap SAFEs, assume no MFN election because the alleged later terms are not better at a $25M pre-money Series A, assume no promised options, and target a 12% fully diluted option pool after the $8M Series A. The five cap percentages sum to 29.583% before the Series A. The 2M existing pool is 16.667% of the stated 12M shares, not 15%.

One consistent model produces:

• SAFE shares before the pool increase: approximately 5.041M, using 12M x 0.2958333 / (1 - 0.2958333)
• New option-pool shares: approximately 0.831M, under the stated fully diluted 12% target and pool convention
• Founder ownership after the $8M Series A: approximately 42.4%
• SAFE holders together: approximately 21.4% post-money; Series A investor: approximately 24.2%

This is an illustrative model, not a legal conclusion. A different option-pool definition, promised-option balance, pre-money SAFE, customized MFN clause, discount conversion, charter, or share-price convention changes the result. At exit, liquidation preferences decide who actually gets paid, so conversion percentages alone are not exit proceeds.

Founder ownership should be modeled from every SAFE's legal terms, capitalization records, and financing assumptions. The number of SAFEs is less important than the definitions and interactions.

What Negotiation Levers Still Exist After SAFEs Are Signed?

Once SAFEs are signed, their agreed conversion rights generally remain in the documents, but the new financing can still be negotiated. The parties may negotiate valuation, the size and timing of an option-pool refresh, new-money allocation, and whether optional pro rata rights are exercised.

The four highest-leverage Series A levers when you walk in with stacked SAFEs:

1. Option-pool sizing and timing. Confirm whether the requested target is calculated before or after the financing and which holders bear the refresh.
2. Pre-money valuation. Model how the proposed valuation affects the priced-round price and each SAFE's cap-versus-discount result.
3. New-money allocation. Confirm the primary investment, any secondary transaction, and how the round changes the capitalization.
4. Optional pro rata rights. YC describes pro rata as an optional side letter, not an automatic feature of every SAFE. Model it only if the right exists and is exercised.

Walk into the Series A with a reproducible waterfall and reconcile it to the cap-table model, signed documents, and counsel's review. That gives you a defensible number without assuming that any software output or fixed discrepancy range is universally wrong.

What Are the Most Common Stacked SAFE Modeling Mistakes?

Common modeling errors include using the wrong SAFE version, omitting converting securities from a post-money Company Capitalization, ignoring discounts or document-specific MFN elections, treating an option-pool refresh as if it were outside the priced-round capitalization, and failing to model optional pro rata participation.

1. Using the wrong form version. Read the operative definitions, not only the first-page label.
2. Omitting converting securities. Standard post-money Company Capitalization can include converting securities without double counting.
3. Ignoring document-specific rights. Check discounts, MFN elections, promised options, side letters, and optional pro rata participation.
4. Misstating the option-pool refresh. Define the target, timing, and fully diluted denominator in the financing documents.
5. Treating a model output as the ground truth. Carta and Pulley publish tools for multiple SAFEs and priced rounds. Reconcile any output to signed instruments, capitalization data, financing terms, and qualified counsel.

When Do You Need More Than a Spreadsheet?

A spreadsheet can model a simple set of instruments if its assumptions match the signed documents and the formulas are independently checked. Complexity increases when the cap table mixes pre-money and post-money SAFEs, discounts, MFN language, notes, promised options, pool refreshes, pro rata participation, or customized financing terms.

TILT's Capital Waterfall Model (CapFall) gives founders a way to compare a deal-specific waterfall with their cap-table model. Use a reproducible model, then reconcile it to the legal documents rather than relying on a fixed SAFE count.

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