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Due Date From Start Date Calculator

Work out due date from start date instantly with clear inputs, formula shown and shareable results.

About Due Date From Start Date Calculator

Twenty working days from 1 April 2026 is 29 April - 28 calendar days, because four weekends intervene. Contracts that specify working days therefore run about 40% longer in calendar terms than the number suggests, which is why the day type must always be stated explicitly.

Formulas

Working day due date

add days one at a time, skipping Saturdays and Sundays

Calendar due date

due = start + days

Worked example

With the default values below, Due Date From Start Date Calculator returns Calendar Days Consumed of 28. Change any input above and every figure here is recalculated in your browser.

Inputs used

Start date
2026-04-01
Turnaround allowedaccepts 0–100,000 days
20 days
Count inone of Working days, Calendar days
Working days

Results

Calendar Days Consumed
28 days
Due Date
2026-04-29
Day Of The Week It Falls On
Wednesday
Days Counted
20

Step by step

  1. 1Values used
  2. 2Working day due date
  3. 3Calendar due date
  4. 4Calendar Days Consumed= 28 days
  5. 5Due Date= 2026-04-29
  6. 6Day Of The Week It Falls On= Wednesday
  7. 7Days Counted= 20

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Which convention do contracts use?

It varies, and the difference is material - 20 working days is 28 calendar days. Always check whether the contract says business days or just days.

Does the start day count?

Here counting begins the day after the start date, which is the usual convention for notice and turnaround periods.

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