Julian Day Conversion

Overview

Dates are converted with the standard integer algorithm for the proleptic Gregorian calendar: the Gregorian rules are applied to every year, including years before 1582, and no switch to the Julian calendar is made. `julianDayNumber` is the integer JDN of the given date, which by astronomical convention labels the day beginning at noon UT, so 2024-03-15 is 2460385. The reverse direction uses the matching inverse algorithm and also returns `year`, `month` and `day` as separate numbers.

`modifiedJulianDate` is calculated as JDN minus 2400000.5, so it always ends in .5 and corresponds to noon UT on that date; subtract 0.5 more for the MJD at midnight. `dayOfWeek` is taken from JDN modulo 7, with JDN 0 being a Monday.

`weekNumber` is the ISO 8601 week, where weeks start on Monday and week 1 contains the year's first Thursday, so dates in early January can fall in week 52 or 53 of the previous year. `dayOfYear` runs from 1 to 366. Years 0 to 99 are handled as those years rather than as 1900 to 1999. `daysFromToday` is the JDN minus today's JDN by the server's clock, negative for past dates; it is null on the Free plan. Send either `date` in `YYYY-MM-DD` form or `jdn` as an integer; when both are present, `date` is used.

Live Test Julian Day Conversion Source →

Formula

One function covers the whole catalog: the first argument names the source, the next are its inputs, and the field after them says which single value lands in the cell. Formulas covers the grammar that applies to all of them.

=VERVE("julianday", A2, "gregorian")

=VERVE.CALL("julianday", A2, "gregorian")

A2 holds the date you are looking up. Drag the formula down and each row resolves on its own.

With literal values

Nothing has to come from a cell — typed values work the same way.

=VERVE("julianday", "2024-03-15", "gregorian")

=VERVE.CALL("julianday", "2024-03-15", "gregorian")

Inputs

Required inputs are positional, in the order below, followed by the field. Everything else is passed as a "name", value pair after that — the same shape as SUMIFS. Premium inputs are accepted on every plan but only take effect on plans that include them.

What lands in your sheet

The field — the argument after the inputs — is what makes the formula resolve to one cell. Its value is a dot-path from the table below, so swapping it is how you pull a different value — one formula per column.

Seeing everything at once

Leave the field out and the formula returns the whole response instead: two columns, field name on the left and value on the right, spilling from the cell you typed in.

=VERVE("julianday", A2)

=VERVE.CALL("julianday", A2)

Response fields

Paths are relative to data. Each one is exactly what the field argument accepts, so swapping it is how you pull a different value into a cell. On a plan without a Premium field the cell reads #PREMIUM(field) rather than a value, so a locked field never looks like a real answer.

Filling a whole column

Both platforms make one batched call for a column rather than one request per cell, and both cost the same — 1 credit per row looked up. How you write it differs, because the two runtimes batch at different points.

=VERVE("julianday", A2:A100, "gregorian")

In Google Sheets, give the arguments ranges and the answers spill down from the cell you typed in. Custom functions there run synchronously and in isolation, so dragged cells cannot be coalesced — the range form is how a column becomes one call. The field is required here: a per-row two-column table has nowhere to spill. Use a full column per input (A2:A100, not A2) — a single-cell reference is read as row 1 only and the rest of the column comes back blank.

In Excel, type the formula once and fill down — no range form and none needed, because its runtime is asynchronous and the add-in coalesces the calls a fill produces into a single batched request. Do not hand VERVE.CALL a range: Excel flattens it into positional arguments, so A2:A100 arrives as a hundred separate arguments and the cell reads #ERR rather than filling.

Either way, column A holds your date values and the answers land beside them, one row each, blank rows skipped.

When a cell doesn't fill

A failed lookup returns readable text starting with #ERR rather than a spreadsheet error, because Excel cannot show a custom message on a real error — you would get a bare #VALUE! with no reason. The trade-off is that IFERROR() will not catch it; test with LEFT(cell, 4) = "#ERR" instead. Error handling covers the rest.

Before the formula works

The add-in reads the API key you saved once in the side panel — the key never goes in the formula, so a shared sheet does not leak it and a collaborator without access simply sees the last calculated values.

1. Install the add-in for Google Sheets or Excel.
2. Open the side panel and sign in, or paste a key from your dashboard.
3. Type the formula above into any cell.

Use cases

Astronomical Software

Calculate precise day numbers for celestial events

Historical Research

Convert historical dates to a unified day count

Date Arithmetic

Calculate day differences across long time spans

Scientific Applications

Use continuous day counts for time series data

Other ways to use Julian Day Conversion

Set up Julian Day Conversion on VerveSheets, or reach the same source a different way. Your VerveSheets account and credits work on all of them — one key, one balance.

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