Dollar Cost Averaging Calculator

What this calculator does

This calculator projects what a regular investing schedule builds. Enter the amount you invest each period, how often you invest, the annual return you expect, and the number of years, and it returns the final portfolio value, the total you contributed, and how much of the balance came from investment returns rather than your own money.

That last split is the useful output. Watching contributions and returns diverge over time shows where the crossover sits — the point at which your portfolio grows more from market returns in a year than from anything you add. Reaching that point is the real milestone in a long investing plan.

When to use it

Use it when you are setting up or reviewing an automatic investing schedule and want to know where it leads. Deciding between $400 and $600 a month into an index fund, checking whether your current contribution supports a retirement number, or seeing what ten years of a modest schedule actually produces are all this calculation.

It is also the honest counterweight to the lump sum question. If you have $60,000 sitting in cash, run it as a lump sum in the compound interest calculator and as a spread schedule here, and compare. The gap you see is what you are paying for peace of mind — sometimes that price is worth it, and seeing it explicitly is better than guessing.

Understanding the inputs

Deposit amount and frequency define the schedule. Daily, weekly, monthly, and yearly are all supported, and results are close enough between them that you should choose whatever matches your pay cycle rather than optimizing frequency.

Annual return is the assumption that drives everything, so be deliberate about it. A broad US equity index has returned roughly 10 percent nominal over the long run; 7 percent is the conservative planning figure most advisers use, and it already gives you room for a mediocre decade. Investment period is where the leverage really sits — extending from ten years to twenty roughly triples the outcome for the same monthly commitment.

How is this calculated?

FV = PMT × ((1 + r)^n − 1) / r, where PMT is the monthly-equivalent deposit, r is the monthly rate, and n is the total months.

A worked example

Invest $500 a month for ten years at an assumed 8 percent annual return. You contribute $60,000 and end with roughly $91,500, meaning investment returns supplied about $31,500 — a little over a third of the balance.

Run the same $500 for twenty years and the picture changes shape entirely. Contributions double to $120,000, but the ending value is around $294,500, so returns now account for roughly $174,500 — nearly 60 percent of the total. The second ten years added about $203,000 against the first ten years' $91,500, from identical monthly deposits. That asymmetry is the entire argument for starting early.

Limitations and assumptions

The most important caveat is structural: this model applies a flat, constant return every period, which is not how markets work and is not how dollar cost averaging actually operates. The strategy's core mechanism — buying more shares when prices fall — requires volatility, and a constant-return model has none. Treat the output as a compounding projection, not a simulation.

Past returns do not predict future ones, and any single ten or twenty year window can land well above or below the long-run average. The calculator also excludes taxes on dividends and realized gains, fund expense ratios, and inflation, all of which reduce what you keep. Nothing here is investment advice.