Pregnancy Conception Calculator

Estimate your conception date and last menstrual period from your due date. Free, instant, no signup.

How to use the Pregnancy Conception Calculator

  1. Enter your values. Fill in the fields with your numbers.
  2. Calculate. Press Calculate to run the pregnancy conception calculator.
  3. Use the result. Copy the result or try a related tool next.

Why use our Pregnancy Conception Calculator

Instant results. Enter your figures and the pregnancy conception calculator returns an answer in seconds.
Free & private. Runs in your browser — no signup, and nothing is sent to a server.
Accurate. Uses standard formulas so you can rely on the numbers.

Free to use — premium coming soon

FREE
  • Unlimited calculations
  • Instant results
  • No signup
PREMIUM
  • Remove ads
  • Save & compare scenarios
  • Export results

About the Pregnancy Conception Calculator

The Pregnancy Conception Calculator works backward from a date you already know to estimate when conception most likely happened. Feed it the first day of your last menstrual period (LMP), an estimated due date from your doctor, or an early ultrasound reading, and it returns a probable conception date plus a short window of days when intercourse could have led to pregnancy. Because the body does not announce the exact moment an egg is fertilized, the tool deliberately gives a range rather than a single guaranteed day, which is the honest way to handle a biological event that nobody can pinpoint after the fact.

Reach for this calculator when you are curious which days matter, when you want to estimate gestational age, or when a clinician has given you a due date and you would like to reverse-engineer the timeline. Expectant parents often use it to map the rough first week of pregnancy, to understand a scan that reports something like "8 weeks 3 days," or simply to satisfy the natural question of when it all began. It is also commonly used to narrow down a possible intercourse window, though it can never settle paternity on its own.

Under the hood it relies on standard obstetric arithmetic. From an LMP it applies Conception Date = LMP + (cycle length minus 14), because ovulation typically falls about 14 days before the next expected period. From a due date it subtracts 266 days (38 weeks), the conventional gestation length counted from conception. From an ultrasound it works from the measured gestational age back to the ovulation window. It then widens the result by a few days on each side to account for sperm surviving in the reproductive tract for roughly 3 to 5 days.

Treat every result as an educated estimate, not a medical record. Ovulation timing shifts with cycle length, stress, and individual variation, so the LMP method is least reliable for irregular cycles. An early first-trimester ultrasound (best between 6 and 8 weeks) is the most accurate dating method, usually correct within 5 to 7 days. The calculator runs entirely in your browser: the dates you enter are never sent to a server, stored, or shared, so you can explore a sensitive question privately.

Frequently asked questions

How accurate is the conception date this calculator gives?

It is a reasonable estimate, not an exact date. Because ovulation and fertilization timing vary between people and cycles, the tool returns a window of a few days. An early ultrasound dated between 6 and 8 weeks is the most accurate method and is typically correct within 5 to 7 days.

Which input gives the best result: last period, due date, or ultrasound?

An early first-trimester ultrasound is the most reliable, since it measures the fetus directly. A doctor-provided due date is the next best. The last menstrual period works well only if your cycles are regular and you know the first day accurately.

Why does it show a range of dates instead of one day?

Sperm can survive in the reproductive tract for about 3 to 5 days, so intercourse on several different days could result in the same pregnancy. The calculator widens the estimate to reflect that fertile window rather than pretending one exact day is certain.

Can this calculator tell me who the father is?

No. It can only suggest a likely conception window, which may overlap with more than one partner if encounters were close together. Only a prenatal or postnatal DNA test can determine paternity definitively.

Do I need a regular cycle for the last-period method to work?

It is most accurate with regular cycles, because the formula assumes ovulation about 14 days before your next period. If your cycles are irregular, enter your true average cycle length, and treat the result as a rough guide or rely on an ultrasound instead.

From our blog

Salary to Hourly: How to Find What Your Time Is Really Worth

By the Super Simple Digital Tools Team · Updated June 2026

A salary hides one important fact: how much you are paid for each hour you actually work. Two people earning $60,000 can have very different deals. One works a steady 40 hours a week and earns about $28.85 an hour; the other routinely puts in 55-hour weeks and is really making closer to $20.98 for the same paycheck. Converting salary to hourly strips away the headline number and shows the rate your time commands, which is the figure that matters when you negotiate, job-hunt, or decide whether a promotion is worth the extra hours.

The core calculation is short. Take your annual salary, then divide it by your hours per week multiplied by your weeks per year. The familiar 2,080-hour benchmark assumes 40 hours across all 52 weeks, but the second number is where most people get it wrong. If you take two weeks of unpaid leave, you work roughly 50 weeks, not 52, so your effective rate is higher than the simple 2,080 division suggests. Adjust the weeks figure to match how much of the year you are genuinely on the clock and the result becomes far more honest.

Schedule length is the other lever. Salaried roles often expect more than 40 hours without extra pay, and every additional hour quietly lowers your real rate. Run the numbers both ways before accepting an offer: calculate the hourly rate at the official 40 hours, then again at the hours the role actually demands. The gap between those two figures is the unpaid premium you would be giving up. For hourly and overtime-eligible roles the reverse is true, since hours beyond 40 can earn time-and-a-half, which a flat salary never does.

Keep in mind that the converted rate is gross. Federal and state income tax, the 6.2% Social Security and 1.45% Medicare FICA contributions, health premiums, and any retirement deductions all come out before money reaches your account, so your net hourly take-home is lower than the calculator shows. On the other side of the ledger, benefits like employer retirement matching, paid holidays, and insurance can add meaningful value that a raw hourly number does not capture. Treat the gross rate as a clean comparison baseline, then layer taxes and benefits on top.

Used this way, salary-to-hourly conversion becomes a decision tool rather than a curiosity. Compare a staff job against a contract gig by putting both on the same hourly footing. Check whether a 10% raise that comes with a heavier workload actually beats your current rate per hour. Price freelance work so it clears your old employed wage after you account for unpaid admin time. The arithmetic takes seconds, but the perspective it gives on your real earning power lasts well beyond a single calculation.

  • Use the real hours you work, not the contracted 40, so an offer that expects long weeks shows its true lower hourly rate.
  • Lower the weeks-per-year figure below 52 to reflect any unpaid time off, which raises your effective rate.
  • Remember the result is gross; estimate roughly 20-35% off for income tax and the 7.65% FICA total to gauge take-home.
  • When comparing offers, add the value of benefits and overtime separately, since the hourly number alone leaves them out.

Read the full guide →

Tool by the Super Simple Digital Tools Team. Reviewed by our editorial team. Free to use, no signup required.

Related tools