Add a List and Inspect Every Subtotal

Add a list without hiding the path

The addition calculator accepts an ordered list rather than one expression. It begins at zero and adds each finite decimal in sequence. The result includes every subtotal, so a user can locate the row where an unexpected total first appears.

Enter one value per line. Negative addends are allowed and reduce the running total. Zero remains a real row. Optional labels can identify public categories such as materials or credit, but labels never enter the arithmetic and should not contain private names or account details.

Why row order still matters for review

Addition is commutative: changing the order of finite addends does not change the exact final sum. The subtotal trail does change. That trail can make a list easier to reconcile with another source, identify a sign mistake, or group related values.

Reverse rows is therefore a review action. It immediately marks the existing trail stale and waits for Add values. If the exact final sum changes after reversal, there is a defect or an invalid state, because rational addition should preserve it.

Blank-line handling is explicit. Ignore blank lines supports pasted lists with spacing. Report blank positions treats every blank as an input problem. The selected policy appears in the result header.

Worked example: positive charges and one credit

Enter these four lines in order:

18.75

12.40

-5.15

3

The trail begins 0 + 18.75 = 18.75. The second subtotal is 31.15. Adding the negative value gives 26.00. The final addend produces 29.00. Exact rational sum is 29/1; displayed sum is 29 under Exact mode.

The contribution counts are three positive, one negative, and zero zero-valued rows. The largest absolute contribution is 18.75. That field describes magnitude only; it does not say that the row is important or correct.

Reverse the list and calculate again. The stages become 3, -2.15, 10.25, and 29, while the final exact sum remains 29. This is a useful demonstration of stable totals and order-dependent subtotals.

Preserve entered decimals as rationals

Each finite decimal becomes an integer coefficient over a power of ten. 18.75 is 75/4; 12.40 reduces to 62/5; -5.15 reduces to -103/20; and 3 is 3/1. Adding reduced rational values avoids treating binary floating-point artifacts as the sum.

Exact mode removes unnecessary trailing zeros while keeping the fraction available. A selected decimal display rounds each visible subtotal and the final decimal under the half-away-from-zero display rule. Internally, later stages use exact values, not the rounded text from the previous row.

This distinction matters: visually summing rounded subtotals can differ from rendering the exact final sum. The copy output labels rounded values and includes the exact total.

Use labels without turning the tool into a ledger

Labels are temporary display aids. They do not create accounts, categories, receipts, dates, or a saved register. Avoid customer names, invoice identifiers, health information, payment references, or confidential project labels. row 1, materials, and credit are sufficient for a safe example.

The site does not import a file or spreadsheet. Paste plain numbers only after verifying their separators. A comma-formatted value such as 1,250.00 is rejected rather than interpreted under an unknown locale.

Distinguish addition from ordered subtraction

Adding -5 is algebraically equivalent to subtracting 5, but the interface purpose differs. Use this page when every row is an addend whose sign is already part of the data. Use the subtraction calculator when there is one starting value and a series of explicit “subtract this” actions.

The basic calculator is better for two values. The running tape is better for a sequence of different operations. No state moves automatically between these pages.

Limits and interpretation

The tool accepts 2–30 lines and bounded decimal length. It rejects fractions written with slashes, expressions, currency signs, units, exponent notation, and non-finite values. The subtotal trail cannot validate that a pasted row belongs in the list or carries the correct sign.

Do not use the result as an accounting system, bank reconciliation, tax calculation, medication total, grade book, or regulated record. Keep the source list and apply appropriate review.

Addition questions

Enter two or more addends and select Build the subtotal trail. Compare each stage with the source list, inspect negative signs and blank handling, and copy the labeled trail only when the final sum and rows are understood.