How to use this new average calculator
Update an average after adding new observations without re-entering the original dataset. Supply the old average, how many values it represents, and the new values. The result reconstructs the old total, adds the new total, and divides by the combined count.
- Enter the old average values in the labeled fields, using consistent units.
- Load the example to inspect the expected format, then replace it with your own values.
- Select Calculate and check the result alongside its working. Reset starts a fresh calculation.
New Average formula
New mean = (old mean × old count + sum of new values) ÷ (old count + new count)
The old count controls how much a new result can move the mean. A single new score changes an average based on four observations much more than one based on four hundred. This tool adds observations; it does not replace existing ones.
Follow the numbers
An average of 75 across 4 results has total 300. Add 95: (300 + 95) ÷ 5 = 79.
Load the example above to inspect the entries, then change one value and calculate again. The result follows your selected method. Display rounding changes how the answer is shown; it does not change the underlying observations or weights.
What to check before using the result
A rounded old mean creates an approximate new mean. Use the original total or unrounded mean when available.
Keep enough precision in the source values for your task. A result calculated from rounded summaries can only be as precise as those summaries. If a number was mistyped or an observation is missing, correct the inputs and calculate again before copying or exporting the answer.
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Common mistakes to avoid
- Confusing a blank with zero. A real zero is an observation. Missing information is not automatically zero.
- Mixing incompatible scales. Use consistent units, or normalize values before combining them.
- Rounding too early. Keep the original values and round at the result stage.
- Using the wrong weighting. A rounded old mean creates an approximate new mean. Use the original total or unrounded mean when available.
Frequently asked questions
What formula does this calculator use?
New mean = (old mean × old count + sum of new values) ÷ (old count + new count). An average of 75 across 4 results has total 300. Add 95: (300 + 95) ÷ 5 = 79.
What should I check about the method?
A rounded old mean creates an approximate new mean. Use the original total or unrounded mean when available.
How many entries can I use?
Paste up to 10,000 values, or use up to 100 individual rows when the chosen input method supports them. Numbers must be finite and no greater than 1 trillion in magnitude. Group and old-count inputs have additional whole-number requirements.
Are the displayed decimals exact?
The calculation uses standard floating-point numbers and compensated addition. Results are rounded only for display. Very small values use scientific notation so they do not silently appear as zero. Select the display precision you need, while respecting the accuracy of your original data.
Are my entries saved or sent anywhere?
The calculator performs its arithmetic in your browser. It does not automatically store entries or send them to a server. Copy, print, and CSV actions happen only when you choose them.
Read our calculation methodology for supported precision, validation, and assumptions.