SWP Corpus Calculator
A regular SWP (Systematic Withdrawal Plan) calculator tells you how long a given corpus will last if you withdraw a fixed amount every month. The SWP Corpus Calculator works the other way around — it tells you exactly how much you need to invest today so that a chosen monthly withdrawal lasts for your desired number of years, at your expected rate of return.
This is especially useful for retirement planning: instead of guessing how much you need to save, you can work backward from the monthly income you want and find the exact lump sum required. Simply enter your desired monthly withdrawal amount, your expected annual return rate, and how many years you want the withdrawals to last.
SWP Corpus Calculator Formula
The required corpus is calculated using the present value of an annuity formula, which finds the lump sum needed today to fund a series of equal monthly withdrawals:
Required Corpus = W × [ 1 − (1 + i)^−n ] / i
Where:
- W = Monthly withdrawal amount you want
- i = Expected monthly rate of return (annual rate ÷ 12 ÷ 100)
- n = Total number of months you want the withdrawals to continue (years × 12)
This formula calculates the corpus needed so that the balance is exactly exhausted after the chosen number of years — it assumes you’re fine with the corpus reaching zero at the end of the period.
If instead you never want the corpus to run out — living only off the returns while the principal stays intact — a different, larger corpus is needed:
Perpetual Corpus = W / i
This perpetual corpus formula assumes the withdrawal amount is fully covered by the monthly return generated, so the principal itself is never touched.
Example Calculation
Suppose you want a monthly withdrawal of ₹10,000 to last for 20 years, assuming an expected annual return of 8%.
- Monthly Withdrawal (W): ₹10,000
- Expected Annual Return: 8% (Monthly rate i = 0.667%)
- Withdrawal Period: 20 years (n = 240 months)
Using the annuity formula:
Required Corpus = 10,000 × [ 1 − (1.00667)^−240 ] / 0.00667 ≈ ₹11,95,543
| Metric | Details |
|---|---|
| Required Corpus (depleting) | ≈ ₹11,95,543 |
| Total Withdrawal over 20 years | ₹24,00,000 (₹10,000 × 240 months) |
| Corpus for Perpetual Income | ≈ ₹15,00,000 (never runs out) |
So investing approximately ₹11,95,543 today, at an expected 8% annual return, would let you withdraw ₹10,000 every month for 20 years, with the corpus reducing to zero right at the end. If you’d rather never touch your principal and keep withdrawing ₹10,000 a month indefinitely, you would need a larger corpus of approximately ₹15,00,000 instead.
FAQs about SWP Corpus Calculator
What is a SWP Corpus Calculator?
A SWP Corpus Calculator tells you how much lump sum you need to invest today in order to withdraw a fixed monthly amount for a chosen number of years, based on an expected annual rate of return. It is the reverse calculation of a regular SWP calculator, which instead tells you how long an existing corpus will last.
What is the difference between the ‘Required Corpus’ and ‘Corpus for Perpetual Income’ figures?
The Required Corpus is the amount needed so your monthly withdrawals exactly exhaust the investment by the end of your chosen period — the balance reaches zero at that point. The Corpus for Perpetual Income is a larger amount calculated so the monthly withdrawal is fully covered by the returns generated, meaning the principal is never touched and withdrawals could theoretically continue forever.
Is the required corpus guaranteed to last the exact number of years?
Only if your investment actually earns the expected rate of return you entered, consistently, throughout the withdrawal period. Since mutual fund and market-linked returns fluctuate year to year, actual results can differ from this projection — the calculator provides an estimate based on your assumed average annual return.
How does the expected return rate affect the required corpus?
A higher expected return rate reduces the corpus you need, since your investment does more of the work through growth, while a lower return rate increases the required corpus, since more of the withdrawal has to come directly from the principal.
Should I use a conservative or aggressive return assumption for retirement planning?
For long-term retirement income planning, it’s generally advisable to use a conservative return assumption rather than the highest historical return you’ve seen, since underestimating your required corpus can leave you short of income in later years. Many planners also recommend building in a buffer above the calculated figure for unexpected expenses or lower-than-expected returns.
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