Dollar-cost averaging calculator
Average price and outcome when buying the same amount at regular intervals.
Fill in the fields and the result will appear here automatically.
Works out what happens when you put the same sum in every month at a changing price. A fixed amount buys more units when the price is low than when it is high, so the average purchase price comes out NO GREATER THAN the average price over the period — that is a property of the harmonic mean rather than an effect of the strategy itself. Price growth here is an assumption you edit, not a forecast: the calculator does not know future prices and will not present them as known. The final value is taken at the last purchase price, and the table shows how the units piled up month by month.
How it works
Formula and logic
Purchases occur at the start of n whole months: units = constant contribution / current price. Between purchases multiply the price by (1 + monthly change / 100); there is no additional change after the last purchase. Invested = contribution × n, average price = invested / accumulated units, final value = units × last purchase price. The average purchase price is no greater than the arithmetic mean of positive prices; they are equal for a constant price. The range is 1–12000 months and a change strictly above −100%; numerical overflow stops the calculation.
Example
Contribute 10,000 at the start of each of 12 months, starting at price 5,000 with a 2% change between purchases: this buys 21.574 units at an average price of 5,562.33 and a final value of 134,120.90 at the last purchase price.
Fields and units
- Monthly contribution — $
- Months — months
- Starting price per unit — $
- Monthly price change, % — unitless
How to use
- — Enter the amount you invest each month.
- — Enter how many months the purchases continue.
- — Enter the price per unit at the start.
- — Set the assumed monthly price change — negative for a decline.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- Investor.gov, US SEC: equal amounts at regular intervals and units purchased
- Limitation
- Equal contributions and a constant assumed monthly price change form a scenario, not a forecast or profit guarantee. Fees and taxes are excluded; purchase costs can change the actual all-in average cost. Fractional asset units are allowed.
FAQ
Why is the average price below the average price over the period?
Because a fixed sum buys more units when the price is low, so the cheap months carry more weight in the average. This is a property of the harmonic mean and holds whichever way the price moves. If prices are constant, the means are equal.
Is this a forecast of returns?
No. The price growth is a figure you supply, and the calculator simply works through its consequences. It does not know the future price and will not invent one.
Which price is the final value based on?
The last purchase price. Using some later price would mean inventing an extra period you never asked for.
Can I model a falling price?
Yes, enter a negative percentage. Falling 1% a month, 5,000 a month over two years gives an average price of 177.74 against a starting price of 200.
Are fees and taxes included?
Equal contributions and a constant assumed monthly price change form a scenario, not a forecast or profit guarantee. Fees and taxes are excluded; purchase costs can change the actual all-in average cost. Fractional asset units are allowed.