A retirement calculator is an online financial planning tool that estimates the corpus an individual needs to accumulate by their target retirement age to sustain their desired post-retirement lifestyle — and the monthly savings or SIP amount required to reach that corpus target. The calculation incorporates inputs including: current age, target retirement age, current monthly expenses, expected inflation rate, post-retirement life expectancy, expected return on investments during the accumulation phase, and expected return during the drawdown phase. For example, a 30-year-old Indian investor planning to retire at 60 with current monthly expenses of ₹50,000 would need a significantly larger retirement corpus after accounting for 30 years of inflation during the accumulation phase and a 25 to 30-year post-retirement period. Retirement calculators highlight the powerful impact of starting early — a person investing ₹10,000 per month from age 25 accumulates a significantly larger corpus than someone investing ₹25,000 from age 40, despite the latter's higher contribution amount. In India, where traditional joint family support systems are weakening and life expectancy is increasing, retirement planning has become a critical financial priority — making retirement calculators an important tool for initiating goal-based financial conversations and demonstrating the urgency of early, consistent SIP investing.