The Step-Up SIP Compounding Multiplier: Mathematical Framework
Published: August 2026 • Verified Reference
Standard financial calculators assume static monthly investments over multi-decade horizons. In reality, working professionals experience career progression, merit raises, and salary step-ups. Sanchita models this as a discrete growing annuity.
1. Mathematical Recurrence Equation
For each month m ∈ [1, 12 × years]:
Where r_m = (1 + r_pre)^(1/12) - 1 is the monthly effective investment return rate, and P(m) = P_0 × (1 + s)^floor((m - 1) / 12) steps up geometrically every 12 months at annual step-up rate s.
2. Comparative Compounding Impact (20 Years @ 12% CAGR)
| Scenario | Total Invested | Final Corpus | Multiplier |
|---|---|---|---|
| Flat ₹30,000 / month | ₹72.0 Lakhs | ₹2.99 Crores | 4.15× |
| 10% Annual Step-Up SIP | ₹2.06 Crores | ₹6.23 Crores | +108% Wealth |
3. Real Rate of Return (Fisher Equation)
To measure true purchasing power net of inflation:
At 12% equity returns and 6% inflation, real purchasing power growth is approximately 5.66% per annum.
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