If you freelance, you are also your own accounts department — and the accounts department usually gets fired first. Invoices go out from your email, payments arrive whenever, and by month three you genuinely don't know who owes you what.

You don't need accounting software for this. A spreadsheet handles invoice tracking well if you set up three specific columns and two formulas. Here's the whole method.

The columns that matter

Create a sheet with one row per invoice and these columns:

1. Invoice # — sequential (INV-001, INV-002…). Never reuse numbers.
2. Client
3. Description — one line; you'll thank yourself at tax time.
4. Issue date
5. Amount
6. Status — use a dropdown with exactly three values: Sent, Paid, Void. (Data → Data validation in Google Sheets.) Resist adding more statuses — ambiguity is what kills trackers.
7. Due date — calculated, not typed (formula below).
8. Paid date — fill this in the day money lands, not the day someone promises.

The two formulas that do the work

Auto due date. If your payment terms are 14 days, in the Due date column write:

=IF(D2="","",D2+14)

(where D is your Issue-date column). Every invoice now knows its own deadline.

Overdue flag. In a new column:

=IF(AND(F2="Sent", G2<TODAY()), "OVERDUE", "")

(F = Status, G = Due date). Anything unpaid past its due date now flags itself. Sort or filter by this column every Monday — that's your follow-up list.

The habit that makes it work