Simulator
Test a lump sum plus monthly contributions against real historical prices — free, in your browser, with no sign-up.
Pick a stock, an index, or a basket. Choose your dates. Set a starting amount and how much you'll add each month. The simulator runs that plan against real month-end prices and shows what the position would have been worth, right next to the cash you put in. It's the easiest way I know to see how steady monthly buying holds up through both the good runs and the bad ones.
There are three modes. Single follows one stock or index against your contributions. Compare lines up to five tickers against each other on the same scale. Portfolio mixes up to five holdings by weight, with optional monthly rebalancing, always against an S&P 500 benchmark using the same cash flow. To keep things honest it skips taxes, dividends, fees, and slippage — these are historical what-ifs, not advice. New here? Read how it works or browse the learning library.
Guide
The tool answers one question: what would this contribution plan have been worth? Here's how to ask it good questions.
Every run draws two lines: the cash you put in (your starting amount plus each monthly contribution, stacked up over time) and the value of the position those purchases grew into. The gap between them is the whole story. When the value line dips below the cash line, the plan was underwater — and it's worth noticing how long those stretches lasted, because that's the part a return number hides. A plan that finished up 12% a year but spent eighteen months underwater in the middle is a very different experience from a smooth ride to the same endpoint. The most useful thing to take from any run isn't the final figure; it's an honest look at the worst stretch, and whether you'd have kept contributing through it.
Start dates change everything. Run the same monthly plan into the same ticker starting 2016, 2020, and 2022. The ending values differ enormously — not because the plan changed, but because the entry decade did. This is the fastest cure for reading too much into any single backtest, including ours.
The index is the bar to clear. In Portfolio mode the dashed S&P 500 benchmark receives exactly the same cash flow as your basket. Before concluding a hand-picked mix "worked," check whether it beat the boring alternative that required no picking at all. Over most long windows, that bar is higher than people expect.
Volatile winners test your stomach, not just your math. Compare a high-flyer against the index in Compare mode, then look at the drawdowns along the way. Many tickers that finished far ahead spent long stretches down 50% or more from their highs. Holding through that is the price of the ending number — the chart shows you the bill in advance.
The simulator skips taxes, dividends, trading fees, slippage, and fractional-share rules. That keeps the math transparent, but know which way each omission leans: excluding dividends understates returns for dividend payers (meaningfully, for an index held over decades), while excluding taxes and fees overstates what you'd have kept. Prices come from month-end closes (Yahoo Finance data, split-adjusted for single stocks), so intramonth swings don't appear — a crash that recovered within a month is invisible here. Treat every result as a clean historical what-if, not a promise: the full mechanics, per mode, are documented in the help center.
If a run surprises you, that's usually the start of a better question. A single stock crushed the index? Check what the same plan did starting two years later. A basket underperformed? Try the same weights with rebalancing on, and see how much the discipline itself contributed. Want the systematic version of that discipline — ranking the whole S&P 500 by momentum, size, or volatility on a schedule? That's the Quant Lab. And if terms like drawdown, rebalancing, or diversification are new, the learning library covers each in plain English, while the DCA guide and risk checklist turn simulator results into an actual plan.