Why Excel Formulas Break and How to Avoid It

An Excel formula worked for months — then suddenly shows the wrong total.

Or #REF!, or just an old number. And the report already went to the client.

Common Causes

• Inserting rows in the wrong place — the SUM range shifted and some expenses dropped out of the calculation;
• Copying a sheet — the formula points to a cell in another file or an old sheet;
• Manual edit of the "total" cell — someone overwrote the formula with a number and the file no longer recalculates.

All three look the same from outside: the file opens, no errors, wrong number.

A Different Approach

In linked tables, expense totals are not a cell range but an aggregation over a relation:

SUM(expenses.amount)

Each expense is tied to a project. Add a record — it enters the sum. Delete it — it leaves. No need to watch range B2:B47.

Explicit Errors Instead of Silent Ones

A broken Excel formula can stay quiet.

In a system with explicit formulas:

• you see which fields build the calculation;
• configuration errors show up during setup;
• changing a field does not break a "link between files" — the link is between tables.

Fewer hidden failures — more predictability.

Summary

Excel is fine for one-off calculations. But when a formula drives operational decisions — budget, estimate, commission — explicit structure with formulas over linked data is more reliable than cell ranges.