Retirement readiness is a single intimidating question -- will the money last? -- and this calculator attacks it from the accumulation side. Starting from where you are today, it compounds your current savings and every future monthly deposit at your expected return until your target retirement age, then reports the pile you will have built, what you contributed, and what compounding contributed.

The defaults tell a familiar American story: 30 years old, retiring at 60, $500,000 already saved -- perhaps a 401(k) with an employer match -- adding $10,000 a month at 12 percent. Thirty years of that recipe produces a staggering figure, most of it gains rather than deposits. Change the return to a sober 8 percent and watch the total nearly halve; that sensitivity is the most important lesson on the page, because nobody earns 12 percent every year for three decades.

Use the tool as a gap analyzer rather than a fortune teller. If the projected wealth falls short of 25 times your desired annual spending -- the rough 4-percent-rule target -- the fix is almost always more monthly savings or more working years, not a riskier portfolio. Small increases early beat heroic increases late: an extra $200 a month from age 30 outweighs an extra $800 a month from age 50.

With the pre-filled defaults — Current Age (years) 30, Target Retirement Age (years) 60, Current Savings ($) 500,000, Monthly Savings ($) 10,000, Expected Annual Return (%) 12 — the Wealth Calculator returns Investment Period (years) 30, Total Amount Invested ($) 4,100,000.00, Wealth Accumulated ($) 53,273,958.40, Wealth Gained ($) 49,173,958.40. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.