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Recurring Event Dates Calculator

Work out recurring event dates instantly with clear inputs, formula shown and shareable results.

About Recurring Event Dates Calculator

A fixed-interval series has n-1 gaps between n occurrences, which is where off-by-one errors creep in. Ten fortnightly events from 12 January 2026 span 126 days and finish on 18 May, not 140 days later. A 14 day cycle repeats about 26.1 times a year, which is why fortnightly payrolls have an occasional three-payment month.

Formulas

Last occurrence

last = first + interval x (occurrences - 1)

Annual frequency

per year = 365.25 / interval

Worked example

With the default values below, Recurring Event Dates Calculator returns Span From First To Last of 126. Change any input above and every figure here is recalculated in your browser.

Inputs used

First occurrence
2026-01-12
Interval between occurrencesminimum 1 days
14 days
Number of occurrencesminimum 1
10

Results

Span From First To Last
126 days
Date Of The Last Occurrence
2026-05-18
Date Of The Second Occurrence
2026-01-26
Occurrences Per Year At That Interval
26.09

Step by step

  1. 1Values used
  2. 2Last occurrence
  3. 3Annual frequency
  4. 4Span From First To Last= 126 days
  5. 5Date Of The Last Occurrence= 2026-05-18
  6. 6Date Of The Second Occurrence= 2026-01-26
  7. 7Occurrences Per Year At That Interval= 26.09

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 2 decimal places, 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

Why is the span not interval times occurrences?

Because the first occurrence is at day zero. Ten events at 14 day spacing have nine gaps, so 126 days rather than 140.

Why do fortnightly cycles give 27 payments some years?

Because 26 fortnights are 364 days, so the cycle drifts forward one or two days a year and eventually a 27th falls inside the calendar year.

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