How this instrument works
A Systematic Withdrawal Plan, or SWP, is the Indian mutual-fund industry's term for taking a fixed sum out of a fund on a set schedule — typically monthly — while whatever remains stays invested and keeps earning a return. It is the mirror image of a SIP: where a Systematic Investment Plan builds a balance from a stream of small deposits, an SWP spends one down through a stream of fixed withdrawals. The person running one is usually not adding to the pot any more — a retiree living off savings built over a career, an investor turning a matured SIP or a lumpsum redemption into monthly income, or someone who sold a property or a business and wants the proceeds paid out like a salary. This instrument does not decide what that monthly figure should be; it takes the withdrawal as fixed and answers what is left over — how many months of income does that fixed number actually buy.
The underlying arithmetic is the same present-value annuity formula that prices a loan or an immediate annuity, solved for the one variable those calculators usually treat as fixed: the count of periods. Starting corpus, ₹ stands in for the present value, Monthly withdrawal, ₹ for the level payment coming out, and Expected annual return, % — divided by twelve and by a hundred to become a monthly rate — for the interest applied to whatever is left after each draw. Because that remaining amount keeps compounding between withdrawals, the fund lasts far longer than a flat division of corpus by withdrawal would suggest; the natural logarithm in the formula is what converts a compounding process into a count of months instead of a plain average.
Two things are worth knowing before reading Months until the corpus is exhausted as a plan rather than an estimate. First, the formula assumes Expected annual return, % holds exactly steady every month, when a real fund's monthly return swings between gains and losses — a run of weak months early on can exhaust a balance sooner than a flat average implies, a hazard finance calls sequence-of-returns risk. Second, if Monthly withdrawal, ₹ sits at or below the interest the corpus earns in a typical month on its own, the withdrawals never actually erode the principal, and the formula has no finite month count to give back — the fund is being lived off, not spent down. Taxes on redemption, exit loads, and fund expenses sit outside this arithmetic too, and each one shrinks what an SWP truly delivers.
- Enter the lump sum you are drawing from into Starting corpus, ₹ — the balance on day one.
- Set Monthly withdrawal, ₹ to the fixed amount you plan to take out every month, rain or shine in the market.
- Type the yearly growth rate you expect the remaining balance to keep earning into Expected annual return, %.
- Read Months until the corpus is exhausted — the point the formula predicts the fund reaches zero.
Worked example — a ₹1,000,000 corpus paying ₹10,000 a month
Take Starting corpus, ₹ at 1,000,000, Monthly withdrawal, ₹ at 10,000, and Expected annual return, % at 8. The monthly rate works out to r = 8 ÷ 1200 = 0.0066667, and the corpus's own monthly interest at that rate is ₹6,666.67 — below the ₹10,000 being withdrawn, so the balance is guaranteed to run down over time rather than sustain itself. Working the formula through gives n = 165.34054113, which the sheet reports as roughly 165.3 months, or just under 13.8 years, before Months until the corpus is exhausted reaches zero.
Compare that to what a plain division would give: ₹1,000,000 shared evenly across ₹10,000 withdrawals, with no return assumed at all, lasts exactly 100 months, about 8.3 years. The extra 65 months — nearly five and a half more years — come entirely from the 8% return still being credited to the shrinking balance between draws. Raise the withdrawal to ₹15,000 a month on the same starting figure and rate, and the runway falls to about 88.5 months, near 7.4 years: the withdrawal amount moves the answer far more sharply than a same-sized nudge to the rate would, because it is being measured against the fund every single month, compounding included.
Questions
What is a Systematic Withdrawal Plan, and who typically sets one up?
An SWP pays a fixed amount out of a mutual fund on a schedule, usually monthly, while the rest stays invested. It suits someone who already holds the balance rather than someone still building one — a retiree living off savings, an investor turning a matured SIP or a lumpsum redemption into monthly income, or anyone who received a large sum and wants it paid out on a schedule instead of sitting untouched.
Why does the fund last longer than corpus divided by withdrawal would suggest?
Because the amount left in the fund keeps earning Expected annual return, % between withdrawals, so growth is covering part of each draw, not just the principal. On the golden example, ₹1,000,000 ÷ ₹10,000 gives 100 months with no growth assumed, but the actual answer is 165.34 months — the gap is entirely the interest still being credited to whatever remains.
What happens if the withdrawal is smaller than the corpus's own monthly return?
Then the balance is never actually depleted — it is being lived off, not spent down, and the formula has no finite month count to return, since the value inside its logarithm would sit at zero or below. That threshold is the corpus multiplied by the monthly rate; keeping Monthly withdrawal, ₹ under it is the arithmetic definition of a payout a fund can sustain indefinitely, assuming the return holds.
How is an SWP different from a SIP?
They are opposite operations on the same kind of fund. A SIP takes a stream of fixed deposits and asks what balance they build into over time; an SWP takes an existing balance and a stream of fixed withdrawals and asks how long it lasts. One accumulates, the other depletes, and a corpus can be built with a SIP for years and drawn down later with an SWP without either calculation needing to reference the other.
Does a higher assumed return always stretch the payout further?
Yes. Holding Starting corpus, ₹ and Monthly withdrawal, ₹ fixed, raising Expected annual return, % always increases Months until the corpus is exhausted, because more of every draw gets offset by growth instead of coming straight out of principal. Even a modest rate above the level that would let a withdrawal sustain itself forever can stretch a depleting fund by years, since that small surplus works in its favor every month.
Does this tell me how much I can safely withdraw each month?
No. The instrument takes Monthly withdrawal, ₹ as a number already decided and reports how long that specific figure lasts under one steady, assumed return — it does not recommend a withdrawal amount, a safe withdrawal rate, or a fund to hold it in. Try a few different figures side by side to see how sharply the runway responds, then weigh that against how long the income actually needs to last.
References
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.