T Nation

Half Life Calculations

SO, for the sake of learning, interest and something to do while i am off work - i have decided to make a Testosterone propionate Half life accurate model.
It is going to be the first 4 or so weeks of a cycle, because 12 weeks with a cyp ester would take - oh, about a month.

This gets very confusing, but look into it and it will allow you to visualize and understand what was once before a very difficult and alien idea.

Some of the advanced guys will know this, but hopefully they wont have seen it written, so i hope this may become a sticky!! lol!
We will be using 100mg of Prop, EOD Sun, Tue, Thu for a total of 300mg a week, this is low but it is near enough to a real cycle (unlike 100mg 1x p/w which would be much easier to write!) for real world applications. The half life of PROP is 4.5 days, for this model i will make it 4… give me a break huh? This is alot of work!

As for the maths… half life works like this:

If the half life is 4 days, the 100mg is half the original active dose in 4 days, 4 days after that that half is halved again, 4 days later, another half. It is simple enough, but it gets complicated when looking at the additions of more and more of the drug and the breakdown of those doses too!

S- 100MG = 100mg
M- > >87mg = 87mg
T- 100MG+75mg = 175mg
WK1W- > >87mg+62mg = 149mg
T- 100MG+75mg+50mg = 225mg
F- > >87mg+62mg+44mg = 193mg
S- 75mg+50mg+38mg = 163mg

S- 100MG+67mg+44mg+31mg = 242mg
M- > >87mg+50mg+38mg+25mg = 200mg
T- 100MG+75mg+44mg+31mg+22mg = 272mg
WK2W- > >87mg+67mg+38mg+25mg+18mg = 235
T- 100MG+75mg+50mg+31mg+22mg+15mg = 293
F- > >87mg+67mg+44mg+25mg+18mg+12mg = 253
S- 75mg+50mg+38mg+22mg+15mg+10mg = 210

S- 100MG+67mg+44mg+31mg+18mg+12mg+9mg = 281
M- > >87mg+50mg+38mg+25mg+15mg+10mg+7mg = 232
T- 100MG+75mg+44mg+31mg+22mg+12mg+9mg+6mg = 299
WK3W- > >87mg+67mg+38mg+25mg+18mg+10mg+7mg+5mg = 257
T- 100MG+75mg+50mg+31mg+22mg+15mg+9mg+6mg+5mg = 313
F- > >87mg+67mg+44mg+25mg+18mg+12mg+7mg+5mg+4mg = 269
S- 75mg+50mg+38mg+22mg+15mg+10mg+6mg+5mg+3mg = 224

S- 100MG+67mg+44mg+31mg+18mg+12mg+9mg+5mg+4mg+3mg = 293
M- > >87mg+50mg+38mg+25mg+15mg+10mg+7mg+5mg+3mg+2mg
T- 100MG+75mg+44mg+31mg+22mg+12mg+9mg+6mg+4mg+3mg+2mg=308
WK4W- > >87mg+67mg+38mg+25mg+18mg+10mg+7mg+5mg+3mg+2mg
T- 100MG+75mg+50mg+31mg+22mg+15mg+9mg+6mg+5mg+3mg+2mg=313
F- > >87mg+67mg+44mg+25mg+18mg+12mg+7mg+5mg+4mg+2mg
S- 75mg+50mg+38mg+22mg+15mg+10mg+6mg+4mg++3mg = 223

S- 100MG+67mg+44mg+31mg+18mg+12mg+9mg+5mg+3mg+3mg = 292
M- > >87mg+50mg+38mg+25mg+15mg+10mg+7mg+5mg+3mg = 240


Very good post. I think I might have some stuff to add, just don’t wanna mess up your thread.

Edit, the info I was reading on was on depot test and blood serum levels. Sorry.

Go for it, i dont mind fella…!

Great post JJ.


I may actually write a bit of code to calculate this for any given dose/half life combination if that would be useful to anyone?

Yeah!! Great idea!

Glad you like.

I’m thinking a few fields to fill in -

1 - Dose in mg
2 - Half life of ester (Doesn’t matter what the actual ester is as long as we know the half life).
3 - Injection frequency
4 - Total length of cycle

Am I missing anything there? I’m tired and not thinking straight!

This would be able to produce a chart just as you have but for any given cycle length. Should be easy enough to produce a graph of the results for easy reading too.

I’ll do some work on it over the next few days and see what I can come up with.

JJ, if you or anyone else can think of any additional features just let me know.

dont we need to have the ester name so you can look up… Undeclynate for example, and it will show you the time when the highest dose is achieved, the best time for PCT, the best inj. freq…

Or havent i got the right idea?!


I see where you are going with that but it wouldn’t strictly be required to do the calculations. It would definately speed up finding out the best frequencies though.

I was thinking that anyone coming to use such a module would already know best injection frequency, the half life of the compound they are using, etc. although it would be nice to get those values filled in automatically (with an option to overide some values to allow for experimentation).

Likewise for when to start PCT. It’s outside the scope of the module really (maybe it’s just me thinking like a programmer).

Maybe I should do the table calculations in one part of the system (that would allow the user to experiment with slightly different inj. freq, dose etc), and then wrap it up in a database of compounds, their half lives, recommended PCT time and any other drug info we could put in there.

I know the profiles for all the compounds I use and have used in the past but if anyone could point me at a definitive list or start posting up details then it would make this a whole lot easier!




Gonna try to dig up some more info, trying to pack my clothes too! Hurray holiday!

Another good calculator…


Cheers guys. These are all good and plenty of great information but I think I can put something together to beat the lot.

There are parts that I can see are missing from each so if I spend a bit of time on it I reckon I can come up with something special.

I’ll do an initial calculator to mimic JJ’s first post plus a graph and then expand it from there.

Should be fairly quick to get to the first stage but further development will take a bit of time. I think it will be well worth doing though - especially with input from the vet’s here.

My problem with these calculators is the very notion of what exactly the half life is. I still follow the rule of carbon atoms multiplied by .7 to give to the half life in days. Prop is 2 days not 4 as JJ asserted in the OP. Enanthate IMO is 5 days under this formula.

This flies in the face of all the half-life charts out there. Until you realize all the half-life charts are merely copies of each other.

In real life if you plan your pins and pct off the x.7 formula you will be much better off.

[quote]saps wrote:
My problem with these calculators is the very notion of what exactly the half life is. I still follow the rule of carbon atoms multiplied by .7 to give to the half life in days. Prop is 2 days not 4 as JJ asserted in the OP. Enanthate IMO is 5 days under this formula.

This flies in the face of all the half-life charts out there. Until you realize all the half-life charts are merely copies of each other.

In real life if you plan your pins and pct off the x.7 formula you will be much better off.[/quote]

This is why I was going to allow for modification of the half life field and get the system to calculate rather than use any sort of lookup tables.

It would allow you to use whatever more exact half life you like for any ester.

I’d not heard the .7 formula before - thanks for the info.

This post was flagged by the community and is temporarily hidden.

[quote]bushidobadboy wrote:
I like the possible outcomes from this thread, plus it’s good to se the rentboy back again, but I have to say that I for one don’t put much faith into half-lives, since the accepted scienc doesn’t sometimes equate to reality.

For example, cyp is only one carbon chain longer than enan, yet for me, takes MUCH longer to be felt.


Hi mate - it is good to be back!

I think really that any calculator like this has got to be used as a rough guide only, but then again we all know that it’s an important part of taking AAS to understand peak levels - so if all this does is give an appreciation of whats going on in a reasonably accurate way then it’s all good.

Everybody is different anyway - I, as you, find Cyp takes ages longer to kick in but a couple of guys I know think I’m talking crap because when they use it they get similar effects to enan.

Mind you, several of the muppets at my gym don’t even know what a half life is - scary really. Some of them ask and if they do I will tell them what I know and point them here. Others are not bothered and just keep banging in shots with no thought. Ahh well - natural selection should sort those guys out.

Anyhow I’ve just spent the last half hour building tables and filling data into them in a MySQL database so now I can start on the enjoyable bit of actually writing some code.

Well- It begins…

Imports DotNetNuke
Imports DotNetNuke.Security.Roles
Imports System.Collections.Generic

Namespace JMIT.JMITHalfLifePCTCalculator

Partial Class HalfLifePCTCalculator

    Inherits Entities.Modules.PortalModuleBase

    Dim BaseHalfLife As Double()

    Protected Sub Page_Load(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles MyBase.Load, Me.Load
            tbHalfLife.Text = ddlEster.SelectedValue
        Catch exc As Exception
            Exceptions.ProcessModuleLoadException(Me, exc)
        End Try
    End Sub

    Protected Sub ddlEster_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlEster.SelectedIndexChanged

        tbHalfLife.Text = ddlEster.SelectedValue

    End Sub

    Protected Sub btnCalculate_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnCalculate.Click

        'Ok - Lets kick some ass!

        'First - Given that the system only allows for set injection frequencies and set dose - we can work out a
        'single complete half life table and then use that offset against itself to add up the other injections.

    End Sub
End Class

End Namespace

Am i just being thick here or has the OP assumed that the half life of his compound is linear? Is it me or do compounds decay in a non-linear fashion, as in, if the half life of a compound was 2 days, and you injected 100mg of it day 1, yes after 2 days there would be 50mg left, but after 1 day there wouldn’t be 75mg left…see what i mean?

Sureley it depends on the order of the reaction as to how the compound would lose its pharmacologic activity.

I would have thought the half life of test followed a first order reaction where t1/2 = ln2/k. A plot of ln[conc test] vs. time t would give a straight line with a slope of - k.

Or am i just confusing myself?

[quote]Sentinal wrote:
Or am i just confusing myself?[/quote]

No you’re confusing me too :wink:
If you shoot 100mg [forgetting the ester weight] of whatever and it has a four day half life lets say than after 4 days you’d have 50mg left and after 8 days you’d have 25mg left and so on and so forth

so following saps example, over the first 4 days, the 100mg drops to half, so is 50mg, i HAVE done a linear calc. for each 4 day ‘cycle’.

So the first 4 days is a drop of 12.5mg a day… the second 4 days is a reduction of 6.25mg, the third 4 days is a drop of 3.125mg per day…

As i said, this IS linear - but not for the duration of the cycle, as that would be massively wrong, only for the duration of the half life on each cycle, which is accurate enough for that sake of a visual graph doncha think?