Investment Calculator

Three engines, not one

Every long-run investment result is the sum of three parts: the starting amount compounding on its own, the stream of contributions compounding from the day each one lands, and the growth on top of both. Early on, the starting amount dominates. In the middle years, your contributions do. Near the end, compound growth outpaces everything — which is why the last decade of a long plan often adds more than the first three combined, even with identical contributions.

Contribution timing is a small, real difference

Contributing at the start of each period rather than the end gives every dollar one extra period of growth. Over a long horizon this adds a fraction of a percent to the final balance — real, but far smaller than the effect of the return rate or the contribution amount. The table above uses your chosen timing.

The return rate is an assumption, not a promise

A single fixed rate is a planning convenience. Real returns arrive in an unpredictable order, and the sequence matters most near retirement when the balance is largest. Use a conservative rate for planning, and treat any single projection as the middle of a wide range rather than a forecast.

Where tax actually lands

The optional tax field here applies once to total growth, which models a taxable account sold at the end. Real taxation is more granular: dividends and realized gains are taxed as they occur in a brokerage account, while tax-advantaged accounts defer or eliminate that drag. A 401(k) or traditional IRA postpones tax until withdrawal; a Roth IRA pays it up front and then grows tax free. For those specific wrappers, use the dedicated pages rather than a flat end-of-life tax.

Frequently Asked Questions