How Much FD Corpus Do I Need to Never Touch the Principal?

You are 55, you want to retire next year, and the only question you keep coming back to is the size of the fixed deposit corpus that lets you live off the interest forever. Before any math, you need to know what is interest rate doing today and what it has done historically, because the answer depends on both numbers more than most people realise.

This guide walks through the exact corpus math, the tax adjustments most calculators skip, and how to stress-test the number so you never have to break the principal.

The basic math: monthly income from FD interest

Start with the cleanest version of the math. If you want a monthly income of X rupees from an FD earning Y percent per year, the corpus you need is roughly:

Corpus = (Monthly income × 12) ÷ Annual interest rate

So if you want 50,000 rupees a month and the bank offers 7 percent, the corpus is (50,000 × 12) ÷ 0.07 = approximately 85.7 lakh rupees. Sounds simple, but this number misses several real-world costs.

The three adjustments most people skip

The pure math overstates how much your FD income actually puts in your hand. Apply these three adjustments:

• Tax on FD interest is paid at your income slab rate. Senior citizens get a 50,000 rupee per year exemption under Section 80TTB; for the rest, every rupee of interest is taxable.
• Inflation erodes purchasing power. A 7 percent FD return with 5 percent inflation is really a 2 percent real return.
• TDS is deducted at 10 percent on interest above 40,000 rupees in a year (50,000 rupees for seniors). It is recoverable at filing time, but it dents monthly cash flow.

What is interest rate doing right now

The repo rate set by the Reserve Bank of India is the anchor for everything else. In 2024-2025, the repo rate has hovered between 6.0 and 6.5 percent. Bank fixed deposit rates for general citizens have therefore ranged between 6.5 and 7.5 percent, with senior citizens getting an extra 0.5 percent.

How rate cycles change the corpus you need

The interest rate cycle is real. In 2017-2018, bank FDs touched 8.5 percent. In 2020-2021, they fell to 5.5 percent. The same monthly income goal needed roughly 55 percent more corpus during the low cycle than during the high cycle.

This is why building your retirement plan around the highest-ever rate is dangerous. You should plan around a conservative long-run average, not the rate available the year you retire.

The realistic corpus table

The table below assumes a 7 percent FD rate, 5 percent inflation, and 20 percent effective tax (a common rate for retirees above the senior exemption). Pre-tax figures and post-tax, inflation-adjusted figures sit side by side.

The post-tax, inflation-adjusted column assumes you want today's purchasing power to last 25 years without ever touching the principal. That is the number serious retirement planners use, not the simple pre-tax figure.

A real-world walkthrough

Take a 60-year-old retiree who wants 60,000 rupees a month. Pure FD math says 1.03 crore at 7 percent. Apply real-world costs:

• Interest income: 7.2 lakh per year.
• Less senior citizen exemption: 50,000 rupees.
• Taxable interest: 6.7 lakh, taxed at the 20 percent slab equals 1.34 lakh per year.
• Net income: 5.86 lakh per year, or 48,800 per month.

Short of the 60,000 target by 11,200 rupees a month. To hit the real goal, the corpus needs to rise to roughly 1.27 crore. Inflation adjustment over 25 years pushes the safe number closer to 4 crore for the same lifestyle.

How to protect the principal forever

The single biggest mistake retirees make is treating the FD corpus as static. Inflation is constant. To keep your principal real, you need three habits:

Reinvest part of the interest every year

Roughly 30 percent of the post-tax interest should go back into the corpus to grow it with inflation. Spend the other 70 percent. Over 20 years, this discipline keeps the principal's purchasing power flat instead of slowly shrinking.

Ladder your FDs

Split the corpus across 1, 2, 3, and 5-year FDs. Each year, one tranche matures and you renew at the prevailing rate. This averages rate cycles and avoids locking the entire corpus at a single low rate.

Keep a separate medical buffer

Do not include medical costs inside the same corpus. Build a separate 10 to 20 lakh pot for medical emergencies on top of health insurance. Pulling from the main FD corpus to fund a hospital bill is how most retirees quietly break the principal.

Review the corpus every year

Once a year, take a quiet evening and recompute the math with the latest FD rate, your updated monthly spending, and the new tax slabs. Inflation might be lower than expected, allowing extra reinvestment. Health costs might be higher, requiring a top-up of the medical buffer. The plan stays alive only when you keep refreshing it. A static retirement plan written five years ago is the most common reason retirees suddenly discover their corpus is shrinking faster than they expected.

For the official repo rate and historical interest rate data, the Reserve Bank of India publishes monthly bulletins. Reading them once a year keeps your retirement plan grounded in real numbers, not assumptions.