How the Retirement Calculator Works
AnyTool Retirement Calculator ties together the two halves of a retirement plan in the browser. In the accumulation phase it grows your current savings plus a monthly contribution at the expected pre-retirement return until your retirement age, using the same reusable, unit-tested investment engine as the SIP and compound-interest tools, and returns a year-by-year schedule and the projected corpus. To size the corpus you need, it inflates your desired annual income (entered in today’s money) to your first year of retirement, then values it two ways: a real-return drawdown that takes the present value at retirement of an inflation-growing income paid for (life expectancy − retirement age) years while the residual balance keeps earning the post-retirement return, and the 4% rule, which sets the corpus at 25× the first-year expense. The gap is projected minus needed — a surplus or a shortfall — and when short, the calculator solves the extra monthly saving that closes it by a monotonic numerical search. All arithmetic is pure client-side JavaScript.
- Accumulation: current savings + monthly contribution compounded monthly at the pre-retirement return
- Desired income entered in today’s money, then inflated to the first retirement year
- Corpus needed = present value of an inflation-growing income (drawdown) OR 25× first-year expense (4% rule)
- Gap = projected corpus − corpus needed → surplus or shortfall
- Extra monthly saving to close a shortfall is solved by bisection on the accumulation engine
