Part of an average’s direction is already known
A 50-day moving average is the mean of the last 50 closing prices. Tomorrow’s calculation removes the oldest close and adds tomorrow’s new close. The old value about to be removed is the deduction value.
Tomorrow’s MA = today’s MA + (tomorrow’s close − deduction value) ÷ number of sessions.
If the deduction value is below the current price, replacing a lower value with a higher one tends to lift the average. If it is above current price, the average tends to decline. This is arithmetic, not a forecast of tomorrow’s market.
Why use 50, 100 and 150 days for US stocks?
The 50-day average is widely watched as an intermediate trend reference in US equities. The 100-day average can help frame intermediate risk, while the 150-day average is common in longer-term trend templates and breadth work. The Moving-Average Deduction page estimates when these averages for the Nasdaq Composite or a top-300 stock could reach a chosen price.
The result is best read as a timing context: if price stays broadly flat, how much time is there before the average approaches it? When an average catches up, price may need to break out, continue consolidating or lose the trend.
Two assumptions, not two forecasts
- Flat: price remains unchanged, producing a slower, upper-bound case.
- Recent 20-session slope: price continues at its recent average pace, offering a second scenario.
With a negative slope, an apparent “catch-up” may occur because price falls into the average rather than the average rises. Always read price direction, average direction and the market backdrop together. Use this as a schedule, not a stand-alone buy or sell signal.