The account cannot answer the question you are asking
A freelancer with one bank account looks at the balance and feels either fine or not fine. That feeling is the only signal available, because the balance is the sum of two unrelated stories: what clients paid, and what living cost.
Margin is what came in minus what it cost to earn — the software subscription, the phone bill, the travel to a client meeting, the share of the electricity bill that belongs to work. In a mixed account those costs sit between a chemist bill and a food delivery, and nobody reconstructs them accurately in April.
So the honest answer to "what do you actually make from freelancing" becomes "about, roughly, I think". Two accounts turn that into a number you can say out loud. Nothing else about the work changes.
Tax arithmetic starts from a figure you must be able to state
Filing as a freelancer begins with gross receipts — everything clients paid you during the year. Under the presumptive scheme for specified professionals, taxable income is taken as 50% of gross receipts, which means the entire computation rests on that single figure being right. Get it wrong and every number after it is wrong by the same amount.
Rebuilding gross receipts from a statement that also holds a rent transfer, an online refund and money a friend returned for dinner is archaeology. Each credit has to be classified from memory, months after the event, by someone who would rather be doing almost anything else.
GST supplies a second reason. Registration becomes compulsory once turnover from supplying services crosses ₹20 lakh in a year — ₹10 lakh in the special category states — and knowing where you stand against that threshold means knowing your receipts as they arrive, not reconstructing them afterwards.
The question you cannot answer from memory
Bank credits are not private in the way people assume. Reporting entities send information about certain transactions to the tax department, and a bank can ask about a deposit under its own customer-verification rules. Neither is a common event and neither is a disaster.
What turns it into a problem is the answer taking a week to assemble. With a separate account the reply is one sentence: that is a payment from this client, here is the invoice, here is the entry against it. With a single mixed account it is an evening of scrolling and a lingering worry that you missed one.
The same logic applies to anything else that asks you to evidence income — a landlord, a lender, a visa application. A statement that reads as a business account reads as a business.
What separation looks like in practice
One account receives client money and pays the costs of doing the work. A transfer moves a set amount to the personal account each month, and that transfer is the salary you pay yourself. Money crosses in one direction only, which is the whole rule.
A share of every client payment gets moved aside for tax on the day it arrives, before it has had time to feel like income. People who do this tend to describe advance tax instalment dates as an administrative chore rather than a shock, which is the entire difference between the two experiences.
None of this requires registering a company, printing letterheads or hiring anyone. It is two accounts, one direction of travel between them, and a habit that takes about four seconds per payment.