Ovulation calculator template

Free build guide: Ovulation calculator for WordPress

This guide rebuilds the Ovulation calculator from this site in Gravity Forms: 3 inputs, 7 live results and no submit button. Expect about 30 minutes by hand. The template above is the same form as an import file, and the bundle adds a PDF version of this guide with a screenshot of every setting, plus the stylesheet.

You will end up with:

• Days until ovulation
• Fertile window opens in (days)
• Fertile window closes in (days)
• Cycle day today
• Ovulation falls on cycle day
• Next period expected in (days)
• Due date if you conceive this cycle

What you need

• Gravity Forms (any license) — Calculation fields are in core; datediff() and today() need GP Advanced Calculations.
• GP Advanced Calculations (Gravity Wiz) — Exponents, functions and date math in calculation fields. The formulas in this template use its syntax. Part of Gravity Perks; needs the Spellbook plugin active as well.

The formulas below use GP Advanced Calculations syntax: exponents, functions or date math that core calculation fields cannot do. Install and activate it, with its Spellbook parent plugin, before you start; without it every result shows 0.

1. Create the form

1. Go to Forms → New Form and name it Ovulation.
2. In Form Settings → Form Layout, set the CSS Class Name to fo-live-only. Step 3 uses it to hide the submit button.
3. Leave the form open in the editor; the fields come next.

2. Add the fields, in this order

Field IDs are assigned as you add fields. If yours come out differently, change the {Label:ID} references in the formulas to match your IDs. Settings not mentioned stay at their defaults.

1. First day of your last period · Date · ID 1
Date Input Type Date Picker; Date Format mm/dd/yyyy; Default Value 10/10/2026.

2. Cycle length (days) · Number · ID 2
Number Format 9,999.99; Default Value 28; Description “First day of one period to the first day of the next. 21–35 is normal; average a few cycles.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

3. Luteal phase (days) · Number · ID 3
Number Format 9,999.99; Default Value 14; Description “Ovulation to the next period. 12–14 for most; leave 14 unless you have tracked it.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

4. Days until ovulation · Number · ID 4
Number Format 9,999.99; Description “Negative means it has passed this cycle. The most likely day, not a guarantee: cycles vary by a few days.”; Custom CSS Class (Appearance tab) fo-result; tick Enable Calculation, Rounding 0.

{Cycle:2} - {Luteal:3} - ( datediff( "1970-01-05", today() ) - datediff( "1970-01-05", {LMP:1} ) )

5. Fertile window opens in (days) · Number · ID 5
Number Format 9,999.99; Description “The five days before ovulation and the day itself.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

{Cycle:2} - {Luteal:3} - 5 - ( datediff( "1970-01-05", today() ) - datediff( "1970-01-05", {LMP:1} ) )

6. Fertile window closes in (days) · Number · ID 6
Number Format 9,999.99; Description “The day after ovulation.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

{Cycle:2} - {Luteal:3} + 1 - ( datediff( "1970-01-05", today() ) - datediff( "1970-01-05", {LMP:1} ) )

7. Cycle day today · Number · ID 7
Number Format 9,999.99; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

( datediff( "1970-01-05", today() ) - datediff( "1970-01-05", {LMP:1} ) ) + 1

8. Ovulation falls on cycle day · Number · ID 8
Number Format 9,999.99; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

{Cycle:2} - {Luteal:3}

9. Next period expected in (days) · Number · ID 9
Number Format 9,999.99; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

{Cycle:2} - ( datediff( "1970-01-05", today() ) - datediff( "1970-01-05", {LMP:1} ) )

10. Due date if you conceive this cycle · Number · ID 10
Number Format 9,999.99; Description “Ovulation day + 266 days. The Pregnancy due date calculator takes it from there.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub fo-result--date; tick Enable Calculation, Rounding 0.

4 + datediff( "1970-01-05", {LMP:1} ) + {Cycle:2} - {Luteal:3} + 266

3. Hide the submit button

The results are live, so nothing needs submitting. Add this filter to your theme’s functions.php or a code-snippets plugin; it hides the button on any form carrying the fo-live-only class:

add_filter( 'gform_submit_button', function ( $button, $form ) {
	return str_contains( (string) rgar( $form, 'cssClass' ), 'fo-live-only' ) ? '' : $button;
}, 10, 2 );

Or with CSS alone: .fo-live-only_wrapper .gform_footer { display: none; }

4. Show the due date if you conceive this cycle as a date

Calculation fields only hold numbers, so the Due date if you conceive this cycle field calculates the number of days since January 1, 1970. A short script turns that number into a date such as “Friday, July 2, 2027” while the field keeps storing the number, so entries and merge tags still work.

1. Keep the Custom CSS Class fo-result fo-result--date on the field, as set in step 2.
2. Load the script on the page with the form: it comes in the template and bundle downloads as date-display.js. Paste it, inside <script> tags, into your site footer with a code-snippets plugin, or enqueue it from your theme after jQuery and Gravity Forms.
3. Preview the form: the result shows as a weekday and date, and a dash until a date is entered.

5. Put it on a page and make it look like this

Add the form to any page with the Gravity Forms block, or the shortcode [gravityform id="X" title="false" ajax="false"]. The form inherits your theme’s styles; the classes you set in step 2 are hooks for the look you see on this site:

• fo-result on a calculation field makes it the big teal result panel.
• fo-result fo-result--sub makes the smaller secondary figures.
• fo-segmented on a radio field turns it into a segmented switch.
• Two fields on one row is the editor’s own column layout: drag a field beside another and the row splits in half. No CSS class is needed, and the old gf_left_half Ready Classes are deprecated.

The bundle includes the two stylesheets that implement those classes, with notes on matching your brand colors. Without them the form still works; it just looks like your theme’s default Gravity Forms styling.

How the math works is explained under “How it’s calculated” on the live Ovulation calculator.