What's a reverse split?

The opposite of a regular split — you end up with fewer, more expensive shares, often used by companies trying to raise their share price to meet an exchange's minimum listing requirement.

Do I owe tax when a stock split happens?

No — a split by itself isn't a taxable event.

Does my broker automatically adjust my cost basis for a split?

For covered securities, yes — brokers are required to track and report adjusted cost basis to the IRS on Form 1099-B.

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Finance

Stock Split Calculator

Post-split share count and adjusted per-share cost basis for a forward or reverse split.

🔒 Runs entirely in your browser — nothing here is ever uploaded

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Last reviewed 2026-08-31

About the Stock Split Calculator

Calculates a stock split's effect on your position — the post-split share count and the adjusted cost basis per share — from your pre-split share count, cost basis per share, and the split ratio.

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How to use it

Enter the number of shares you held before the split, and your cost basis per share.
Enter the split ratio as two numbers (e.g. 2 and 1 for a 2-for-1 split).
Read your post-split share count and adjusted per-share cost basis.

Formula

Split multiplier = new shares ÷ old shares. Post-split shares = pre-split shares × multiplier. Post-split cost basis per share = pre-split cost basis per share ÷ multiplier.

Worked example

100 shares with a $50 per-share cost basis ($5,000 total) undergo a 2-for-1 split: 200 post-split shares at a $25 per-share cost basis, still $5,000 total.

Interpreting your result

A stock split does not change the total value of your position or your total cost basis at the moment it happens. This calculator doesn't handle cash-in-lieu payments some brokers make for a fractional share a reverse split can produce. Not tax advice.

Recommendations

• Your total cost basis never changes from a split alone.
• Reverse splits often signal a company trying to boost its share price to meet a stock exchange's minimum listing price.
• If a split produces a fractional share, most brokers pay you cash for that fraction (cash-in-lieu).

Frequently asked questions

No — a split alone doesn't change your total position value or total cost basis, only how many shares that value is divided across.