Perfect Timing vs Perfect Mistiming

Best Day · Worst Day · 15th of Month · Real Nifty 50 Prices

Loading data … Returns = XIRR, Not CAGR

Section 1

Three Investors, Three Mythical Skills

All three invest the same monthly SIP into Nifty 50 over the same window. Best Day always buys at the month's lowest close (perfect timing). Worst Day always buys at the month's highest close (perfect mistiming). 15th just buys on the 15th (or next trading day). Spoiler: the gap is much smaller than you'd guess.

Monthly SIP ₹

Real Nifty 50 daily closes · …

Best Day — Final Corpus

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XIRR —

15th of Month — Final Corpus

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XIRR —

Worst Day — Final Corpus

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XIRR —

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Why the gap stays narrow

Even perfect within-month timing, an oracle who always bought the cheapest close that month, only beats perfect mistiming by a few percent of XIRR. Why? A SIP buys ~360 times over 30 years. Within any one month, the high-low range is small relative to the long-run trend. The compounding from being invested swamps the day-picking edge.

The 15th-of-month investor, who picked a date once and never thought about it again, lands closer to the perfect-timing oracle than to the mistiming demon. That's the empirical case for just SIPping on a fixed date.

Corpus Growth — Year by Year

All three strategies on the same actual Nifty 50 path. Lines are tighter than intuition expects.

Final Corpus — By Strategy

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Side-by-Side Numbers

Strategy	# SIPs	Total Invested	Avg Buy NAV	Final Corpus	Total Gain	XIRR	vs 15th

📚 Companion research & tools

The SIP Timing Paradox

30 investors, 30 different calendar days, real Nifty 50 prices. Confirms the same thesis: day-of-month doesn't move long-term outcomes.

SIP Frequency Comparison

Monthly vs Weekly vs Daily SIP on real Nifty data. Frequency, like best/worst day picking, is a sub-1% lever.

The SIP Timing Paradox — Research Paper

Walks through why micro-timing decisions don't move long-term outcomes. Best/worst day picking is the extreme stress-test of that thesis.

SIP Scenario Simulator

Vary the entire market regime instead of the within-month timing. Regime moves outcomes; day-picking does not.

Companion Calculator

Investment Calculator

Smooth-CAGR projection on the same inputs. Compare the textbook 12% line to what 30 years of actual Nifty 50 prices delivered, even with perfect timing.

The 50-Day Phenomenon

78% of best days fall during drawdowns. The "best day" of any month is usually after a panic dip — the kind nobody actually times in real life.

The Behavior Tax

Investors who chase "best timing" pay a tax. Even if they could perfectly time within a month, the gain over a fixed-date SIP is small — and the friction cost is large.

The SIP Capacitor

SIPs store volatility. Within-month timing is a microsecond-level adjustment to a long capacitor charge. The math doesn't reward it.

The Coil Principle™

Units accumulated × surge magnitude. Even an oracle's extra units from perfect timing add little to the unit base built over 360+ months.

Duration Matters More Than Magnitude

Same logic at a different scale: depth of crash matters less than time spent recovering. Day-picking, like crash-depth, is a magnitude question; duration dominates.

Wealth Calculator

The variables that do matter: monthly amount, step-up, duration. Each lever moves the corpus by lakhs — orders of magnitude more than perfect day-picking.

The Convergence Lab

Calculator-promised CAGR vs market reality. Even a perfect-timing oracle's XIRR converges to the calculator number — the variance comes from cycle, not from day-picking.