Stock Split Calculator

How to use this stock split calculator

What this calculator does. It converts a pre-split holding into the theoretical post-split share count and price using a new-for-old ratio. It also cross-checks the holding value before and after the split. This is an arithmetic planning tool, not a price forecast, investment recommendation, tax calculation, or statement of how a broker will handle fractional shares. The SEC's plain-language stock split explanation confirms the core identity: a split increases the number of shares without changing shareholders' equity merely because of the split.

When to use it. Use it to translate a company announcement into your expected share count, to compare a forward split with a reverse split, to check the adjusted per-share cost basis before reviewing broker records, or to prepare a clean before-and-after worksheet for your own records. Market prices can move immediately after the effective time, so the calculated price is the mechanical split-adjusted price, not a guaranteed trading quote.

How to calculate. The calculator opens with a complete demonstration: 10 shares at $100 each and a 5-for-2 split. A validated Excel workbook is available immediately. (1) Replace Shares before split with your current holding. (2) Enter the Share price before split in U.S. dollars. (3) Enter the company's announced ratio as New shares in ratio and Old shares in ratio. (4) Read the live outputs and comparison table. (5) Select Download Excel to export the current inputs and results. Reset clears the demonstration and calculated content; Excel export stays disabled until all four required fields contain a complete valid state again.

Input guide. Shares before split is a required positive number of shares; decimals are accepted for fractional holdings, for example 10 or 10.5. Raising it increases both the after-split count and total holding value, but does not change either per-share price. Do not enter commas as decimal separators. Share price before split is a required positive USD amount, such as 100.00. It drives the post-split price and both holding-value figures. A dollar sign and standard thousands separators are accepted, but scientific notation and ambiguous decimal-comma formats are rejected. New shares in ratio and Old shares in ratio are required positive numbers. For 5-for-2, enter 5 and 2; for a 1-for-10 reverse split, enter 1 and 10. Reversing these entries reverses the economic direction of the split.

Output guide. Shares after split equals the original shares multiplied by the split factor. Share price after split is the mechanically adjusted price, calculated by dividing the old price by that same factor. Holding value before and Holding value after are exact arithmetic identities under the model and should match apart from negligible floating-point presentation differences. Theoretical value change should therefore display $0.00. The summary pills classify the event as a forward split, reverse split, or unchanged 1-for-1 ratio, show the factor, and state whether value is preserved. The comparison table repeats the canonical before-and-after shares, price, and value used in the Excel workbook.

Worked example. With 10 shares priced at $100 and a 5-for-2 ratio, the split factor is 5 ÷ 2 = 2.5. Shares after split are 10 × 2.5 = 25. The theoretical price is $100 ÷ 2.5 = $40. The holding value is $1,000 before the split and 25 × $40 = $1,000 after it, so the theoretical value change is $0.00. Those figures match the first-open controls, results, comparison table, and workbook checkpoints.