Apps that calculate Zakat on shares often ask whether you are holding for the long term or the short term. The question matters for Zakat, because scholars treat the two intentions differently. It does not change purification.
Short term: shares as trade goods
If you buy shares to sell them at a profit, they are treated like goods held for trade. Zakat is due at 2.5% of their full market value, once you hold wealth above the nisab for a lunar year. Most scholars follow this view for traders.
Long term: shares as an investment
If you buy for dividends or growth and do not intend to trade, many scholars say Zakat is due on your share of the company's zakatable assets, meaning roughly its cash, receivables and inventory less its short-term liabilities, rather than on the full price. The company's factories, buildings and equipment are not counted. This can be a much smaller figure. Some scholars apply the full-value method even to long-term holders, and it is the more cautious choice.
Why purification is different
Purification depends on the company's impermissible income and on whether you owned the shares at the end of its financial period. How you plan to use the shares does not enter the calculation. See how to calculate it.
How Sanad shows it
The calculator on a stock's Financials tab asks why you hold the stock and shows both figures, so you can see the difference. For some companies, such as banks, the zakatable-assets figure is not reported, and the long-term estimate is not available.
This is an estimate. The scholarly views differ, so follow the ruling of a scholar you trust.