Calendar, Aging, & Fertility

(This is a Sims 4 gameplay post)

After much thought about different ways my sims could age and time could progress, I adopted the system that Laura at Postcards from Sierra Nova has created for Sims 4 aging in her world.  She is incredibly analytical and never fails to come up with an efficient and effective systematic way to manage different games (Sims 2, Sims 3, Sims 4).  So even after months of trying to figure all this out for myself, I preferred her solutions with some small tweaks.


I am using a nifty spreadsheet Laura designed (customized for the current time period in Simdale Valley).  This  is how I will keep track of the calendar, holidays, birthdays, plan/record which households are played when, and keep track of the passage of time.  As I play each day, I can mark it off, so I know which month and year it is.  I am so excited about my sims having actual birthdays now!

Simdale Valley Calendar (including birthdays & holidays)

  • Birthdays and many holidays, are, of course, static each year (on the same date).  The number in parentheses is the birth year of that sim.
  • The following holidays vary a little year to year:
    • Easter (2nd Sunday in March)
    • Mother’s Day (1st Sunday in May)
    • Father’s Day (2nd Sunday in June)
    • Thanksgiving (a Thursday in November that is not right at the beginning or right at the end)

The Current Calendar (June 605 – May 606)

  • The blue highlighting means that day has been played.
  • Column E is for holidays, birthdays, and due dates.
  • Column F is for gameplay notes


I don’t plan to blog everything that happens in Simdale Valley!  As things happen that are “newsworthy” or stories develop, I’ll share them on the blog.


I want my sims to age up at a rate that is consistent with “real world” time in each age group.  In contrast, the vanilla Sims 4 game is created to be skewed with relatively short life stages for adults and elders.   I modified the age lengths to match my idea of life stages and also lengthened each age considerably to allow time to play each household during each season or year.  Since I am playing this neighborhood in rotation, I will only play each household approximately 5 days over the span of each “year” of 120 days. (I currently have 22 households).  A very long age span allows me to play each family, each season, while everyone in the neighborhood continues to age each day that I play.

Here’s the  rate at which sims age in Simdale Valley (with aging on for everyone all the time.)

MC Command Center allows the player to choose the length of pregnancy and each age range, so I enter the number in the last column in MC Command Center to set the length of each age.  You can see, it is just 10 days per sim month so one year is 120 days.

NOTE:  As of 1/16/17 Deaderpool hasn’t updated MCCC yet to set the toddler age span.  I’m sure that’s coming soon.  For now, I have all aging turned off.

Now I have created this handy Age Key which I am thrilled about:  it allows me to sort my sims by age, name, birth year, or birth date.  When I put in the target year, either the year I’m currently playing or a year I’m researching for blogging, it automatically figures out the age of each sim and uses conditional formatting to highlight the sims who have a transition birthday that year.


(Again, system thanks to Laura!)

Playable sims each have a current fertility rate.  I plug it in to the MC Command Center woohoo mod settings (Try for Baby and Risky Woohoo rate) when I play that household, or set them as unable to get pregnant/make others pregnant, in CAS, for sims who are infertile due to age or other reasons.     I haven’t checked yet in game, but I think that nonplayable fertility rates for story progression will automatically vary with the playable sims’ rates.  If I am able to set non-playable’s rates separately, I’ll probably set them around 30% for Try for Baby success rate, and 15% for Risky Woohoo, to give me more babies being born in the neighborhood, at least for now.

When playing a household with multiple child-bearing age sims, this system could be thwarted, which is sort of aggravating, but will probably work out most of the time.   Fertility of Sims who are trying for baby will be determined by the process below & plugged in to the try for baby success rate in MC Command Center, and I will probably use the highest of the females on the lot.  Fertility of sims who are not trying for baby will be determined by the process below and plugged in to the MC Command Center risky woohoo rate, which will probably also be the highest rate between the sims.  So the worst scenario would be if more than one female sim in a household is either trying for baby or having risky woohoo and both are forced to use the same rate even though they should have wildly different rates, which hopefully won’t happen very often.  I reserve the right to decide what to do on a case to case basis, in that situation.  The update made to CAS on June 2nd 2016 will help a lot because if a menopausal/post-menopausal sim is in the same household with a sim who is still fertile, I can set the older sim as unable to get pregnant.

Determining the Current Fertility Rate for each sim

Each sim age 12-50 is currently in one or more of the following states of fertility:

  1. birth control (see rates below; this will be entered in MC Command Center as the risky woohoo rate)
  2. ambivalent (50% of TFB age rate with individual factor, this will be the risky rate)
  3. trying for baby (see rates by age below, this will be the try for baby success rate)
  4. unable to conceive (due to being pregnant, 3 mos or less post-partum).  If this sim is the only female of child-bearing age on the lot, 0% will be the risky woohoo rate.
  5. Not sexually active and not yet on Birth Control, uses the fertility rate below (TFB rate) which they should not need unless they suddenly become sexually active.

At the age of 12, individual fertility factor (IFF)  for try for baby is determined by roll of a die:

  1. -50%
  2. -10%
  3. Normal
  4. Normal
  5. +10%
  6. +20%

Birth Control Failure Rates:

birth control effective rates

  • Standard failure rate of birth control is 4%.  It’s a little high, but I figure it is an average of different types.
  • Traits which connote effective use of birth control make it more effective,  failure rate of 1%
  • Traits which connote sloppy use of birth control make it less effective,  failure rate of  8%
  • Sims over 40% have a failure rate of only 2%, because their fertility has declined, and effective users can achieve a 0% pregnancy rate
  • Effective users over 40 can either be set in CAS to be unable to get pregnant, or they can use the MC Command Center birth control.

Try For Baby Success Rates by Age (Or Fertility Rate)

I take the standard rate for the sim’s age, and add or subtract their Individual Fertility Rate (IFF), which was rolled at age 12.  After the age of 40, IFF can only negatively impact fertility, it can’t increase it.

TFB rate





 Vasectomies, Tubal Ligation, and Aging

With the ability to set whether a sim can get pregnant, get others pregnant, or neither, in CAS as of June 2, 2016, sims are now able to have effective vasectomies and tubal ligations, and elder sim females no longer have to worry about getting pregnant.

Males who have had vasectomies:  Winton Gamble

Females who have had their tubes tied:  Sandy Bruty, Alexis JOnes, Imani Gamble, and Sayuri Ono

Changes I made in ages of sims, from Sims 2:

  • I made Moira and Miguel exactly 60 so their days line up perfectly.
  • I made Ethan McElveen, who had just been born in Sims 2, two years older, because I didn’t want Laney to be pregnant all over again and it is impossible to create a baby in CAS.
  • I had to make Jackson and Chloe, and George and Simone a little younger.  This way, George and Simone would fit in the Young Adult age group, so that Jackson and Chloe wouldn’t have to start as Elders, and I could spread out the age ranges just a bit more.

Reference (No longer in use)

Before MC Command Center had the capability to customize age ranges, I played on long with my version of Laura and Dark Gaia’s aging mod.  In the chart below, the Sims Days on Reg columns represents the numbers in  my version of Laura and Dark Gaia’s aging mod.  The game (and the mod) are set to make the long setting four times longer than the regular.  I am keeping this chart as reference in case I need to return to this method of setting age lengths, but MC Command Center is so easy, thank you Deaderpool!

My Aging System



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