Quick answer
Use an online business day calculator for one-off deadline checks and shareable answers. Use Excel WORKDAY or NETWORKDAYS when the calculation is part of a repeatable spreadsheet workflow.
Use a calculator when
- You need a fast answer for an invoice, delivery promise or SLA.
- You want a shareable result without building a spreadsheet.
- You need to check weekends and public holidays quickly.
Use Excel when
- You are calculating many rows at once.
- Your team already manages invoices, payroll or projects in a workbook.
- You need formulas that update automatically when source dates change.
Formula alternatives
=WORKDAY(start_date, days, holidays) adds business days to a date. =NETWORKDAYS(start_date, end_date, holidays) counts business days between dates.
Best practical setup
Use the calculator to sanity-check the rule and the spreadsheet for bulk processing. Keep the holiday list visible in Excel so someone else can audit the calculation later.