Work out what a share trade actually leaves you, with brokerage, STT, exchange fees, stamp duty and GST on both legs, then capital gains tax on the gain that is left.
Can a profitable trade really lose money?
Yes, and it is common on small positions. The flat brokerage and the depository charge do not shrink with the size of the trade, so on five shares they can be several times the gain. This page reports the sell price at which the round trip breaks even, which is the number worth knowing before you place the order rather than after.
Why is the tax lower than my own calculation?
Probably because you taxed the gross gain. Brokerage, STT and the rest are transfer expenses, so they come off the sale value before the gain is worked out. That reduces the tax as well as the profit. This page hands the tax engine the figure after charges, which is what the law asks for.
What decides short term against long term?
The holding period between the purchase and sale dates. Listed equity crosses into long term after twelve months, and the rates on either side are far apart. That is why the dates are inputs here rather than a tenure in years: a sale a day either side of the threshold is taxed under a different section.
Why does the page ask about other gains this year?
Because the long-term exemption is an annual limit shared across every equity gain you book, not an allowance per trade. If you have already used it on an earlier sale, this trade is taxed from the first rupee. Leaving that field at zero assumes the whole exemption is still available and will understate your tax.
Does this cover intraday, futures and options?
No. This is a delivery trade, one buy against one sell. Intraday is taxed as business income rather than as capital gains, and derivatives carry a different charge structure entirely. The brokerage page prices all four segments if you need the charges alone.
What if I bought in several lots?
Work out your average cost first on the stock average page and use that as the buy price. This page prices one purchase against one sale, which is the common case and keeps the tax treatment unambiguous.