Dollar cost averaging
Investing a fixed amount on a fixed schedule whatever the price, so the same money buys more shares when prices are low and fewer when they are high.
Dollar cost averaging commits you to an amount and a schedule instead of to a price. Anyone paying a set sum into a fund every payday is already doing it, named or not. Because the amount is fixed and the price is not, more shares arrive when the market is down, and the average cost per share ends up at or below the simple average of the prices paid.
It covers two situations worth keeping apart. Investing income as it arrives is averaging by circumstance, since there is no lump sum to invest in the first place. Spreading a sum you already hold is a real choice, and it trades expected return for a smaller worst case: money waiting to go in is not invested, and markets have risen over most long stretches, so spreading tends to finish behind investing at once while also removing the chance of committing everything at a peak.
The mistake is selling the method as a way to earn more. Paying a lower average cost than the average price is arithmetic, and it says nothing about whether the holding was worth owning. What a schedule really buys is consistency and protection from a single badly timed decision, which is why payroll investing works: the decision is made once, in advance, instead of every month against the news. The savings goal calculator works in the same regular-contribution terms.