Running Sum Calculator

A running sum is one of those tiny computations you end up needing constantly, and the tiny reason it is so often asked for is also why it is so rarely built nicely: it is just a few lines of arithmetic, but it amplifies whatever you point it at. Paste a list of transactions and the output is a balance history. Paste a list of measurements and the output is how the total trend has evolved. Paste a list of signups and the output is cumulative growth.

Running Sum Calculator does exactly that computation, plus the small amount of context that makes the number useful in real work — min, max, mean, count, total, largest positive change, largest negative change and a chart of the running total over time. Handle integers and floats, ignore blanks, parse commas and newlines.

Underneath the buttons is the small amount of information the system actually requires — what a running sum represents, where negative numbers fit in, why floating-point precision matters — plus practical guidance on how to interpret the result. Everything runs in your browser; nothing is uploaded.

• Any input list: Paste numbers one per line, comma-separated, space-separated or semicolon-separated. Blanks are ignored.
• Integers and floats: Supports negative numbers, currency-style decimals, scientific notation and mixed separators.
• Per-step running sum: Every intermediate total shown alongside the original value, with the running-total column the focus of the output.
• Statistics summary: Min, max, mean, count, total and standard deviation computed once and shown next to the data.
• Outliers highlighted: Largest positive change and largest negative change flagged with their indices.
• Line chart view: Visualise the running total over time to spot trend breaks, big movers and steady slopes.
• Trend direction: A short narrative — rising, falling, mixed, flat — based on the slope of the running sum.
• Three export formats: CSV (running total), JSON array, and a plain text list with original value and running total together.
• Copy or download: Take what you compute without leaving the browser, with nothing uploaded to any server.

1. Paste your numbers. One per line is the most reliable input; comma-separated or space-separated also work.
2. Set the rounding. Default is 10 decimal places, which works for currency and measurement. Increase for scientific precision, decrease for cleaner display.
3. Read the per-step output. Every value of the running sum is shown alongside the input that produced it, indexed for easy reference.
4. Check the statistics summary. Min, max, mean, count, total and a trend direction tell you what the underlying series looks like.
5. Open the chart view. A line view of the running total makes trend breaks and big movers obvious.
6. Copy or download the result. CSV for spreadsheets, JSON for code, plain text for documentation.

Example 1 — Monthly revenue. Paste 12 numbers, one for each month. The running sum is cumulative annual revenue at the end of each month. The chart view shows when growth accelerated or stalled.

Example 2 — Bank transactions. Paste a list of debits and credits as positive and negative numbers. The running sum is the account balance after each transaction. Largest positive change flags a credit, largest negative change flags a debit.

Example 3 — Cumulative inventory. Paste the net change after each restock — positive for inbound, negative for outbound. The running sum is the stock level at every point, useful for spotting when inventory dipped below zero.

Example 4 — Cumulative signups. Paste the daily signup count. The running sum is total signups to date, useful for keeping a public-facing counter up to date without re-counting the whole list.

Example 5 — Performance over time. Paste 30 latency readings, one per day. The running sum tracks total accumulated latency, useful for cumulative SLA reporting where the goal is to keep the slope shallow.

• Stop writing throwaway scripts: Get a clean running-sum table in one click from any list of numbers.
• Spot trend breaks: The chart view makes sudden changes obvious, even in a long series.
• Trust the summary statistics: Min, max, mean, count and standard deviation calculated for the same list, so you have everything in one place.
• Match any consumer: CSV for spreadsheets, JSON for code, plain text for documentation.
• Free and private: No account, no watermark, nothing uploaded.