Most Indian investors start a SIP without fully understanding what happens behind the scenes each month. In this guide, we walk you through the exact mechanics of a Systematic Investment Plan — from KYC and mandate setup to auto-debit, NAV allotment, unit accumulation, and redemption. By the end, you will know precisely what happens when your SIP date arrives, and why it matters for your wealth.

Step 1: KYC and Mandate Setup

Before you can start a SIP, you must complete your KYC (Know Your Customer) verification with a SEBI-registered KRA (KYC Registration Agency) like CAMS-KRA or KFintech-KRA. KYC requires your PAN, proof of identity, proof of address, and a passport-size photograph. Once KYC is done (usually 1–3 days), it is valid across all mutual funds in India — you do not need to repeat it.

Next, you set up a NACH (National Automated Clearing House) mandate with your bank. This is a one-time authorisation that allows the mutual fund to auto-debit your bank account on your SIP date. The mandate specifies the maximum debit amount (usually slightly higher than your SIP, to allow for future step-ups). Once the mandate is approved (5–7 working days), your SIP is ready to run.

Step 2: The SIP Date Arrives

On your chosen SIP date (e.g., the 5th of every month), the mutual fund sends a debit request to your bank via NACH. Your bank checks your account balance; if sufficient, it debits the SIP amount and credits it to the mutual fund. This typically happens by end of business on the SIP date. If your bank account has insufficient funds, the debit fails — there is no penalty from the mutual fund, but your bank may charge a bounce fee of ₹250–500.

Step 3: NAV Allotment

Once the money reaches the mutual fund, units are allotted to you at the NAV of the next business day. For example, if your SIP date is Friday and money reaches the fund on Friday evening, units are allotted at Monday's NAV (because NAVs are calculated at end of each business day, after market close). The number of units you receive equals your investment amount divided by that day's NAV. If NAV is ₹100 and you invested ₹10,000, you get 100 units.

Step 4: Unit Accumulation Over Time

Each month, your SIP buys a different number of units, depending on that month's NAV. When markets are high (NAV is high), you buy fewer units; when markets are low (NAV is low), you buy more units. This is rupee cost averaging — the single biggest advantage of SIPs. Over 5–10 years, your average purchase price tends to be lower than the average NAV, because you bought more units at lower prices.

For example, over 12 months with NAVs ranging from ₹90 to ₹120, a ₹10,000 monthly SIP would buy between 83 and 111 units each month. Your average purchase price would be slightly below the average NAV, because you bought more units at lower prices. A lumpsum investor, by contrast, is locked into the NAV of their single investment date.

Step 5: Watching Your Corpus Grow

The current value of your SIP investment at any time equals: total units accumulated × current NAV. As the NAV rises over time (assuming the underlying portfolio grows), your corpus grows — both because you keep adding units monthly AND because the value of each existing unit rises. This is compounding in action: your returns earn returns, your accumulated units appreciate, and your monthly additions accelerate the growth.

Use our SIP Calculator to project how this growth will look over different time horizons. A ₹10,000 monthly SIP at 12% over 15 years builds approximately ₹50 lakh; over 25 years, it builds about ₹1.9 crore. The same monthly effort, just more time — that is the magic of compounding through SIPs.

Step 6: Pausing, Stopping, or Modifying Your SIP

Open-ended mutual fund SIPs are flexible. You can: (1) Pause your SIP for 1–6 months (most funds allow this) — useful during financial stress. (2) Stop your SIP permanently — no penalty, no impact on existing units. (3) Modify your SIP amount — usually by stopping the existing SIP and starting a new one with the desired amount (some platforms allow in-place modification). (4) Redeem some or all units anytime (except ELSS, which has a 3-year lock-in per instalment).

Step 7: Redemption and Taxation

When you redeem your SIP units, the mutual fund sells them at the day's NAV and credits the proceeds to your bank account — typically within 1–3 working days for equity funds, 1 working day for liquid funds. The redemption triggers capital gains tax: 10% LTCG on gains above ₹1.25 lakh per year (if held 12+ months in equity funds), 20% STCG (if held less). Each SIP instalment has its own holding period, calculated from its allotment date.

Redemptions follow the FIFO (First-In-First-Out) principle — the oldest units are redeemed first. So if you have been running a SIP for 5 years and redeem some units, the units from year 1 are sold first (qualifying for LTCG), not the units from last month (which would be STCG). Strategic redemption planning can help you use the ₹1.25 lakh LTCG exemption each financial year.

What Happens During Market Corrections?

This is where most investors panic — and where SIPs prove their worth. When the market falls 20%, your existing units' value drops 20% temporarily. But your next SIP instalment buys units at the new, lower NAV — meaning you accumulate significantly more units than usual. When the market recovers (as it always has, historically), those cheaply-acquired units appreciate dramatically, accelerating your recovery.

The worst decision you can make during a market correction is to stop your SIP. This locks in your losses, prevents you from buying at low prices, and breaks the rupee cost averaging mechanism. The second-worst decision is to redeem in panic — that converts temporary paper losses into permanent real losses. Stay invested, continue your SIP, and let the market do its job.

Common Operational Issues

Two issues come up frequently: (1) Bounced SIPs due to insufficient balance — fix by maintaining a buffer in your SIP-linked account, or change the SIP date to align with your salary credit. (2) Mandate expiry — NACH mandates have a fixed maximum amount; if you step up your SIP beyond this, you need a fresh mandate. Most platforms alert you in advance. (3) Fund mergers or closures — SEBI occasionally reclassifies funds; your SIP continues in the merged/renamed fund automatically.

Conclusion: The SIP Is a Quiet, Powerful Machine

Once you set up a SIP, it works silently in the background — debiting your account, buying units, accumulating wealth, compounding returns. You do not need to time the market, watch daily NAVs, or make frequent decisions. You just need to fund your account, stay invested, and let time do the heavy lifting. The mechanics are simple, but the long-term results are extraordinary.