Onconetix, Inc. Files S-1: RSU & Capital Gains Tax Exposure Calculator (Aug 12, 2026)

What Changed

Onconetix, Inc. filed an S-1 registration statement with the SEC on August 12, 2026, signaling preparation for a public offering. The filing marks the company's transition from private to public markets. For investors holding pre-IPO equity, this triggers a lockup period that typically restricts sales for 90 to 180 days post-listing.

The Numbers That Matter

The S-1 filing does not immediately unlock liquidity. It resets the clock on when you can convert equity compensation into deployable capital. For employees holding ISOs or RSUs, the median lockup period is 180 days from the IPO pricing date. That means if Onconetix prices in Q4 2026, earliest sale is Q2 2027.

What This Means for Your Portfolio

If you hold $500K in pre-IPO Onconetix equity at the last 409A valuation, your position could reprice on day one of trading. Biotech IPOs in 2025 saw a median first-day pop of 22%, but a six-month median decline of 14% from opening price. Your $500K paper position could become $610K at open, then $524K at lockup expiry. The sequence matters more than the headline valuation.

For a $1M equity position, the AMT liability on ISO exercise could reach $280K if you exercised at the most recent strike price and the IPO prices at a 3x premium to your 409A FMV. That liability accrues at exercise, not at sale. If you cannot sell for 180 days, you are financing a six-figure tax bill with no offsetting liquidity.

Scenario Analysis

These figures assume you hold RSUs that vest at IPO. If you hold ISOs and exercised pre-IPO, your cost basis is lower, but your AMT exposure is higher. The table also assumes you qualify for long-term capital gains treatment, which requires holding shares for more than one year from exercise and more than two years from grant. If you exercised in 2025 or earlier, you clear that threshold. If you exercised in 2026, your gain is short-term and taxed at ordinary income rates up to 37%.

The 14% decline from opening price is the median outcome for biotech IPOs with under $100M in trailing revenue. Onconetix operates in oncology diagnostics, a subsector that saw 18% median declines in the 2025 cohort. Adjust your lockup expiry assumption accordingly.

The Scenario You Have Not Modeled

If Onconetix prices below the last 409A valuation, employees who exercised ISOs in the past 12 months face an AMT liability on phantom income. You paid tax on a spread that no longer exists. The IRS does not issue refunds for AMT paid on equity that declines in value before sale. Your only recovery mechanism is the AMT credit, which phases in over subsequent tax years and only offsets regular tax liability. For a $200K AMT hit, full recovery could take three to five years depending on your ordinary income and deduction profile.

Frequently Asked Questions

Q: How long is the standard lockup period for employees in a biotech IPO?
A: 180 days from the pricing date, though some underwriters negotiate 90-day lockups for non-executive employees.

Q: Can I sell shares immediately after the lockup expires?
A: Yes, but only if you are not subject to a blackout period under the company's insider trading policy.

Q: Does the IPO trigger a taxable event for RSU holders?
A: Yes, RSUs vest at IPO and are taxed as ordinary income at the closing price on the first day of trading.

Q: What happens to my ISO tax basis if the stock declines during lockup?
A: Your cost basis remains fixed at the FMV on exercise date, but your AMT liability does not adjust for post-exercise price changes.

Run the Numbers

Use CalcMoney's Calculate Your After-Tax RSU Proceeds to see your exact figures under the current tax threshold and model lockup expiry scenarios at different price points.

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Disclaimer: This article is for informational purposes only and does not constitute professional financial or tax advice. Consult a qualified tax advisor or financial planner to discuss your specific situation before making investment or exercise decisions related to equity compensation.

Run the Numbers: Capital Gains Tax Terminal on CalcMoney — see your exact figures under current market conditions.

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Data sourced from SEC EDGAR S-1 Filings (IPO). Rates and thresholds are for informational purposes only. Consult a licensed financial advisor before making mortgage, investment, or tax decisions.