What tax do I owe when I sell a flat or land in India?

Selling property triggers capital gains, and the treatment turns on how long you held it. Hold it beyond the long term threshold and the gain is long term, taxed at a concessional rate, otherwise it is short term and added to your regular income. The rules on indexation (adjusting your purchase cost for inflation) were changed recently, so what your uncle did a decade ago may not apply to you now. There are also exemptions if you reinvest the gain into another house or into specified bonds within set timelines, which can legitimately reduce or defer the tax. Property is high value and the paperwork matters, so the cost of a good CA here is trivial next to the tax at stake. Property tax rules and rates shift frequently, so confirm the current position before you sign anything.

A curated summary to orient you, not advice. The resources below are the real value.