{"id":60604,"date":"2015-06-10T08:31:45","date_gmt":"2015-06-10T06:31:45","guid":{"rendered":"https:\/\/wpcalc.com\/?p=60604"},"modified":"2026-09-28T13:51:30","modified_gmt":"2026-09-28T10:51:30","slug":"date-of-conception","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/pregnancy-baby\/date-of-conception\/","title":{"rendered":"Date of Conception Calculator"},"content":{"rendered":"<section class=\"not-prose calculator-box\" aria-labelledby=\"calculator-title\"><div class=\"flex items-baseline sm:items-center justify-between gap-2 sm:gap-3\"><div class=\"flex flex-col sm:flex-row sm:items-center gap-2\"><span class=\"icon icon-calculator text-primary-700! text-base! dark:text-primary-300!\" aria-hidden=\"true\"><\/span><h2 id=\"calculator-title\" class=\"text-lg font-display font-bold\">Estimate Baby Conception Date<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"60604\" data-favorite-title=\"Date of Conception\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/pregnancy-baby\/date-of-conception\/\" data-favorite-excerpt=\"Estimate a conception date from the first day of your last menstrual period, your cycle length, and the length of the second part of your cycle. The displayed date may be one month later than the intended estimate.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-ovum-sperm\">\n    <span class=\"icon icon-shape-star-empty\" aria-hidden=\"true\"><\/span>\n  <\/button>\n  <div class=\"calcdash-favorite__tip\" aria-hidden=\"true\">\n   <span class=\"favorite-tooltip\" id=\"favorite-tooltip\"><\/span>\n  <\/div>\n  <span class=\"sr-only\" role=\"status\" id=\"favorite-status\"><\/span>\n<\/div><\/div><form action=\"https:\/\/wpcalc.com\/en\/pregnancy-baby\/date-of-conception\/\" method=\"POST\" class=\"calculator\" id=\"calculator-60604\" data-post=\"60604\"><fieldset class=\"fieldset-input is-1\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field\" id=\"input-1\"><label for=\"field-1\">First day of your last menstrual period<\/label><input type=\"date\" name=\"first_day_of_your_last_menstrual_period\" id=\"field-1\" step=\"any\" value=\"2026-11-12\"\/><\/div><div class=\"field\" id=\"input-2\"><label for=\"field-2\">Cycle Length<\/label><input type=\"text\" name=\"cycle_length\" id=\"field-2\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"21\" max=\"45\" value=\"28\"\/><\/div><div class=\"field\" id=\"input-3\"><label for=\"field-3\">Second part of the cycle<\/label><input type=\"text\" name=\"second_part_of_the_cycle\" id=\"field-3\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"9\" max=\"16\" value=\"10\"\/><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"60604\">Calculate<\/button><button type=\"reset\">Reset<\/button><\/div><div class=\"field is-checkbox hidden!\" id=\"field-auto-calc\"><input type=\"checkbox\" id=\"auto-calc\"><label for=\"auto-calc\">Calculate automatically<\/label><small>If enabled, the result will update automatically when you change any value.<\/small><\/div><div class=\"fieldset-result is-hidden\" aria-labelledby=\"result-title\" aria-live=\"polite\" role=\"region\"> <h3 class=\"result-title bg-gradient-to-r from-primary-50 to-gray-50 dark:from-primary-900 dark:to-gray-800\" id=\"result-title\"><span class=\"icon icon-s-pulse\" aria-hidden=\"true\"><\/span> Your Results<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>Supposed date of conception<\/span><\/span><span class=\"field-value\" id=\"result-1\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><\/div><div class=\"result-actions\"><button type=\"button\" class=\"copy-link\"><svg viewBox=\"0 0 20 20\" fill=\"currentColor\" aria-hidden=\"true\"><path d=\"M12.232 4.232a2.5 2.5 0 0 1 3.536 3.536l-1.225 1.224a.75.75 0 0 0 1.061 1.06l1.224-1.224a4 4 0 0 0-5.656-5.656l-3 3a4 4 0 0 0 .225 5.865.75.75 0 0 0 .977-1.138 2.5 2.5 0 0 1-.142-3.667l3-3Z\"\/><path d=\"M11.603 7.963a.75.75 0 0 0-.977 1.138 2.5 2.5 0 0 1 .142 3.667l-3 3a2.5 2.5 0 0 1-3.536-3.536l1.225-1.224a.75.75 0 0 0-1.061-1.06l-1.224 1.224a4 4 0 1 0 5.656 5.656l3-3a4 4 0 0 0-.225-5.865Z\"\/><\/svg><span class=\"copy-link__text\">Copy link to this calculation<\/span><\/button><span class=\"sr-only\" role=\"status\" id=\"copy-link-status\"><\/span><\/div><\/div><a href=\"#respond\" class=\"hidden transition-opacity duration-300 opacity-0 w-50 text-sm justify-center items-center gap-2 px-4 py-2 rounded bg-gray-200 text-gray-700 hover:bg-gray-300\" id=\"leave-comment\"><span class=\"icon icon-comments\" aria-hidden=\"true\"><\/span>Leave a Comment<\/a><\/form><\/section><section id=\"calc-reactions\" class=\"not-prose hidden my-12 bg-gradient-to-r from-primary-50 to-gray-50 border border-indigo-100 rounded-xl px-6 py-4 shadow-sm\" data-post=\"60604\" aria-live=\"polite\" aria-labelledby=\"calc-reactions-title\"><p id=\"calc-reactions-title\" class=\"text-sm text-gray-500 text-center mb-2\">How did this result make you feel?<\/p><div role=\"group\" aria-labelledby=\"calc-reactions-title\" class=\"grid grid-cols-3 sm:flex sm:flex-row sm:justify-around gap-4 sm:items-center sm:flex-wrap\"><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"like\"><span class=\"reaction-count\" data-reaction-count=\"like\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude00 <\/span><span class=\"reaction-description font-medium\">Like <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"helpful\"><span class=\"reaction-count\" data-reaction-count=\"helpful\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\udca1 <\/span><span class=\"reaction-description font-medium\">Helpful <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"confused\"><span class=\"reaction-count\" data-reaction-count=\"confused\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude15 <\/span><span class=\"reaction-description font-medium\">Confused <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"disappointed\"><span class=\"reaction-count\" data-reaction-count=\"disappointed\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude1e <\/span><span class=\"reaction-description font-medium\">Disappointed <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"inaccurate\"><span class=\"reaction-count\" data-reaction-count=\"inaccurate\">2<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\u274c <\/span><span class=\"reaction-description font-medium\">Inaccurate <\/span><\/button><\/div><div id=\"reaction-message\" class=\"hidden mt-8 rounded-md border border-primary-100 bg-white\/50 backdrop-blur-sm px-4 py-2 text-sm text-center shadow-sm\"><\/div><\/section><div class=\"calcdash-ad not-prose calcdash-ad--calc_result calcdash-ad--in-article\"><ins class=\"adsbygoogle\" style=\"display:block\" data-ad-client=\"ca-pub-1721569815777345\" data-ad-slot=\"6317458308\" data-ad-layout=\"in-article\" data-ad-format=\"fluid\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script><\/div>\n<style id=\"wpcoderpro-inline-1\">.formula-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section class=\"formula-box\" aria-labelledby=\"formula-title\">\r\n\t<div id=\"formula-title\" class=\"not-prose font-display mb-4\"><span class=\"icon icon-formula\" aria-hidden=\"true\"><\/span><h2>Date of Conception Formula<\/h2><\/div>\r\n\t<figure class=\"not-prose formula\">\r\n\t\t<figcaption class=\"formula-title\">Formula<\/figcaption>\r\n\t\t<div class=\"text-base text-gray-800\" id=\"formula\">\n\\[D_{\\mathrm{shown}}=\\operatorname{JSDate}(Y,M,D)+(C-L)\\text{ days}\\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(D_{\\mathrm{shown}}\\) \u2014 the date currently displayed by the calculator.<\/li>\n<li>\\(Y,M,D\\) \u2014 the year, month, and day entered as the first day of the last menstrual period.<\/li>\n<li>\\(C\\) \u2014 Cycle Length, in days.<\/li>\n<li>\\(L\\) \u2014 Second part of the cycle, in days.<\/li>\n<li>\\(\\operatorname{JSDate}\\) \u2014 the calculator\u2019s date conversion, which treats month numbers as zero-based.<\/li>\n<\/ul>\n<p>The intended estimate is the entered period date plus \\(C-L\\) days. However, the current date conversion treats the entered month as the following month, so the displayed result does not match that intended calculation.<\/p>\n<p>\r\n<\/section>\n<style id=\"wpcoderpro-inline-459\">.calculation-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section id=\"calculation\" class=\"calculation-box\" aria-labelledby=\"calculation-title\">\r\n\t<div id=\"calculation-title\" class=\"not-prose font-display\"><span class=\"icon icon-unordered-list\" aria-hidden=\"true\"><\/span><h2>Date of Conception \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> Enter September 1, 2026, as the First day of your last menstrual period. Keep Cycle Length at 28 days and Second part of the cycle at 10 days.<\/p>\n<p>\\[C-L=28-10=18\\text{ days}\\]<\/p>\n<p>The intended estimate is September 1 plus 18 days: September 19, 2026. The current calculator instead converts the entered date to October 1 before adding those 18 days.<\/p>\n<p>\\[D_{\\mathrm{shown}}=\\text{October 1, 2026}+18\\text{ days}=\\text{October 19, 2026}\\]<\/p>\n<p><strong>Result:<\/strong> the calculator displays October 19, 2026. The intended cycle-based estimate is September 19, 2026.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to use the calculator<\/h2>\n<ol>\n<li>In <strong>First day of your last menstrual period<\/strong>, enter the first day of bleeding in your most recent period, not the day it ended. The field initially shows the current date, so change it if your period began earlier.<\/li>\n<li>In <strong>Cycle Length<\/strong>, enter your usual number of days from the first day of one period to the first day of the next. The default is 28 days; the field accepts 21 to 45 days.<\/li>\n<li>In <strong>Second part of the cycle<\/strong>, enter the estimated number of days from ovulation to your next period. The default is 10 days; the field accepts 9 to 16 days. If you do not know this length, treat the result as a rough estimate.<\/li>\n<li>Read <strong>Supposed date of conception<\/strong>, but check it against the intended calculation: add Cycle Length minus Second part of the cycle to the period date you entered. The current displayed result has a month-conversion error.<\/li>\n<\/ol>\n<h2>What a conception date estimate means<\/h2>\n<p>The calculator uses cycle timing to estimate ovulation, then uses that day as an approximate conception date. If a cycle lasts \\(C\\) days and its second part lasts \\(L\\) days, ovulation is estimated \\(C-L\\) days after the first day of the last period. For example, the default values of 28 and 10 place estimated ovulation 18 days after that first day\u2014not 14 days after it.<\/p>\n<p>Ovulation and conception are related but are not always the same calendar event. An egg is usually available for fertilization for about 12 to 24 hours after ovulation, while sperm can survive in the reproductive tract for up to about five days. Sex several days before ovulation can therefore lead to conception around ovulation. A cycle calculation cannot identify the precise time of fertilization or determine which day of intercourse led to a pregnancy.<\/p>\n<p>Cycle-based dates are useful for understanding the likely timing of pregnancy, but they are not a diagnosis or a confirmed pregnancy date. Pregnancy weeks are conventionally counted from the first day of the last menstrual period rather than from conception. For that distinction, see the <a href=\"https:\/\/wpcalc.com\/en\/pregnancy-baby\/gestational-age\/\">Gestational Age Calculator<\/a>. If you are estimating a birth date instead, use the <a href=\"https:\/\/wpcalc.com\/en\/pregnancy-baby\/pregnancy-due-date\/\">Pregnancy Due Date calculator<\/a>.<\/p>\n<h2>Assumptions and practical limitations<\/h2>\n<p><strong>Check the displayed month.<\/strong> The current implementation passes the entered month number to a date function that expects January to be month zero. As a result, it begins its calculation in the following calendar month. Adding a month is not the same as adding a fixed number of days, and dates near the end of a month can roll over. Until this is corrected, use the entered period date\u2014not the displayed date\u2014as the starting point when checking \\(C-L\\) days manually.<\/p>\n<p>The estimate also assumes that your entered cycle length and second-part length reflect the cycle in question. Ovulation can shift from cycle to cycle, even when periods are generally regular. Irregular cycles, a recent pregnancy, breastfeeding, illness, and some medications can make a calendar-based estimate less reliable. If you track ovulation signs or use ovulation tests, compare those observations with a <a href=\"https:\/\/wpcalc.com\/en\/pregnancy-baby\/fertility-ovulation-calendar-2\/\">Calendar of Ovulation and Fertility<\/a> rather than treating one calculated date as certain.<\/p>\n<p>If the date matters for prenatal care, discuss it with a healthcare professional. An early pregnancy ultrasound may help establish gestational age when menstrual dates are uncertain; neither a cycle calculation nor an ultrasound can usually establish the exact date of fertilization.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Estimate a conception date from the first day of your last menstrual period, your cycle length, and the length of the second part of your cycle. The displayed date may be one month later than the intended estimate.<\/p>\n","protected":false},"author":70,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[45],"tags":[46],"class_list":["post-60604","post","type-post","status-publish","format-standard","hentry","category-pregnancy-baby","tag-fertility-conception"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/60604","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/users\/70"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=60604"}],"version-history":[{"count":3,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/60604\/revisions"}],"predecessor-version":[{"id":65380,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/60604\/revisions\/65380"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=60604"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=60604"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=60604"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}