The provision that has already operated
Two different sections get mixed up here, and the difference decides how you should think about your situation.
Section 8 is voluntary renunciation, open to any citizen of India of full age and capacity. It used to require that you already held another nationality, but those words were removed from the section in 2004. You make a declaration, it is registered, and on registration you cease to be a citizen.
Section 9 is the one that has probably already applied to you. Any citizen of India who voluntarily acquires the citizenship of another country shall, upon such acquisition, cease to be a citizen of India. It is automatic. There is no application, no decision and no discretion.
So if you naturalised in 2019, you have not been an Indian citizen since 2019, whatever the passport in your drawer says.
The word doing the work is voluntarily. Some people do not acquire a citizenship by asking for it. A child naturalised alongside a parent, or someone who gets it automatically under that country's law, is in a different position. For them, whether Section 9 applied at all, and from what date, is a real question, and the date on the naturalisation certificate does not settle it. Have that assessed before you file anything. The renunciation paperwork does not end your citizenship. It records an end that has already happened.
That framing matters, because people delay out of a sense that filing is what triggers the loss. It is not.
If you applied for the other citizenship, stop travelling on the Indian passport today, because on the published mission tables every further trip adds to what you will be charged. If it came to you automatically or as a minor, do not act on this yet: you may still be an Indian citizen, and surrendering would leave you with nothing to travel on.
And do not surrender it until you have settled how you will get into India. Renunciation takes roughly sixty days and the OCI card comes after that. A visa on the foreign passport is the obvious stopgap, but missions commonly ask a former Indian citizen for the surrender or renunciation certificate before issuing one, which is the document you do not yet have. Sort the travel out before you file, not after. People surrender the passport on a Monday and find on the Friday that they cannot fly to a family emergency.
What you actually file, and what you get back
The declaration is made in Form XXII under Rule 23(1) of the Citizenship Rules 2009, through the online citizenship portal, with the Indian passport surrendered.
Two documents come back, and they get conflated. First an acknowledgement in Form XXIII, confirming the mission has uploaded your signed declaration. The certificate itself follows, in Form XXIV under Rule 23(3), and that is the one an OCI application asks for. It goes by two names, and the split is not about when you file. It turns on when you acquired the foreign citizenship. Acquired on or before 31 May 2010, missions charge only a small miscellaneous fee and usually call the document a surrender certificate. Acquired on or after 1 June 2010, a renunciation fee applies and it is usually called a renunciation certificate. Several missions say plainly that the two names mean the same document, and it serves the same purpose in an OCI application either way.
The Ministry indicates about 60 days, counted from when the mission or district office uploads your verified signed hard copy, rather than from your online submission.
Why this blocks your OCI
The renunciation or surrender certificate is a required supporting document for an OCI application. Missions state it directly: on acquisition of foreign citizenship, all Indian nationals should surrender the passport if it was acquired before 31 May 2010, or renounce citizenship after that date.
This is why the question usually arrives in the form of a stuck OCI application rather than as a citizenship question. You cannot go around it, and the sequence is renunciation first, OCI second.
The penalty question, answered honestly
If you travelled on the Indian passport after acquiring foreign citizenship, or simply held on to it, missions levy a penalty. We are not going to give you a single national figure, and here is why.
Two Indian missions publish penalty tables on their own official sites, and the figures are not reconcilable. One sets US$250 for each instance of misuse after a three-month grace period, capped at US$1,250, plus US$250 where the passport was retained beyond three years. Another sets 10,000 rupees for each trip after the grace period, capped at 50,000 rupees, plus a further 25,000 rupees where the Indian passport was reissued after naturalisation. Those are not currency equivalents of each other.
We could not find a single circular that unifies them. The practical answer is that this is administrative, set by consular instruction, and your own mission's published schedule is the one that will apply to you. Read that page, not a summary of it.
A word on Section 12(1A) of the Passports Act, which you will see cited here. It is aimed at a person who is not a citizen applying for or obtaining an Indian passport by suppressing their nationality, or holding a forged passport or travel document, and it carries imprisonment of not less than one year. Simply still holding a genuine Indian passport is not within it. Do not assume it cannot reach you. Once Section 9 has operated you are a non-citizen, so renewing an Indian passport after naturalising without disclosing the new nationality can fall inside it, and that is the range some missions cite.
What missions actually collect for having travelled on an already-issued passport is different in kind: an administrative penalty fixed by consular instruction, not a conviction and not a court sentence. Many mission tables do head those rows Section 12(1A), so do not be surprised to see the number quoted against it. The number that will be charged is the one on your own mission's table.
What changes about your property rights
For buying property, less than people fear. The Reserve Bank treats an NRI and an OCI the same way. Either may acquire immovable property in India, other than agricultural land, plantation property or a farmhouse. The same bar applies to acquiring those by gift.
One point that is widely reported the wrong way round. Citizens of Pakistan, Bangladesh, Sri Lanka, Afghanistan, China, Iran, Nepal, Bhutan, Macau, Hong Kong and North Korea need prior Reserve Bank approval to acquire immovable property in India whatever their residential status. The rule then says expressly that the prohibition does not apply to an OCI. So if you hold both one of those nationalities and an OCI card, the card takes you out of the restriction rather than leaving you inside it.
Inheritance is the exception, and it is an important one. The inheritance provisions carry no agricultural-land carve-out, so an OCI can inherit and hold agricultural land that the deceased had lawfully acquired. Buying it is barred. Inheriting it is not.
The trap is on the way out. Under the foreign-exchange rules, agricultural land, a farmhouse or plantation property can be sold or gifted only to a person resident in India. So you may inherit the farmland and hold it, but your buyer pool is narrow. State land laws can narrow it further, because several states restrict who may buy farmland at all.
What does change is the tax picture, and not because of your citizenship. Indian tax residence turns on days spent in India, so the move abroad rather than the passport is what shifts your position.