CTC ("Cost to Company") is what your employer budgets for you in a year -- it includes your base salary, but also employer contributions the company pays on your behalf, like its share of Provident Fund, plus benefits that may never show up as cash at all, like insurance premiums or a meal card. None of those extra pieces land in your bank account as take-home pay, which is why a big CTC offer rarely translates into an equally big number in hand every month.
What actually gets deducted before you see your salary
From your gross salary (the cash component of CTC, before employer-side extras), a few things typically come out before it hits your account: your own Provident Fund contribution, professional tax where applicable, and TDS -- tax deducted at source. Your employer withholds an estimate of your annual income tax and pays it to the government in monthly installments on your behalf, rather than you paying a lump sum at year-end.
Basic, HRA, and the rest of the breakup
Gross salary itself is usually split into components -- basic salary, House Rent Allowance (HRA), and other allowances -- rather than paid as one flat number. This breakup matters because components are taxed differently: HRA can be partially tax-exempt if you're paying rent and meet the conditions, while a flat "special allowance" is fully taxable. Two people with the identical gross salary can end up with different take-home pay if their basic-to-allowance ratio is structured differently.
Why TDS changes your in-hand pay through the year
TDS isn't a fixed percentage taken off every payslip -- it's your employer's running estimate of your total annual tax, divided across the months left in the financial year. That's why in-hand pay can shift after you submit investment declarations or rent receipts, or after a raise: the employer recalculates the annual estimate and adjusts the monthly TDS accordingly. It's also why the old and new tax regimes matter here -- which one you (or your employer, by default) pick changes how much is withheld each month, not just your final tax bill.
Getting from CTC to a real number
Because the gap between CTC and take-home depends on your specific breakup and deductions, there isn't one universal percentage that converts one to the other -- the honest answer is "it depends on your structure." What you can do is work the actual math for your own numbers instead of estimating with a rule of thumb.
The Salary Calculator converts your salary across annual, monthly, and hourly rates, and the Income Tax Calculator works out your tax liability under both the old and new regime, so you can see where the deductions in your specific case actually come from.