Methodology. Future monthly expenses at retirement = current × (1+inflation)^(years to retirement). Corpus needed = present value of annuity required to cover inflation-adjusted expenses for (life – retirement) years at post-retirement real return (post return minus inflation). Monthly SIP to build corpus uses standard SIP compounding formula. Assumes continuous inflation at given rate. Real-world planning should include lumpy expenses (medical, weddings) and insurance costs separately.