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Welcome to the Urban Worm Calculator!

  • Learn how long it will take for your worms to reproduce
  • Learn how much vermicompost and worm castings they will create
  • Learn how much money your worm stock is worth on a month-to-month basis
  • Understand how many worms you can sell in your business and still maintain or grow your population


The Urban Worm Calculator is completely dependent upon the accuracy of the inputs you provide. Unrealistic input will provide an unrealistic output. Do not use this calculator as a sole source for making any business decisions.

Got Questions about How the Urban Worm Calculator Works?

Read the Urban Worm Calculator Guide

Watch Videos about the Urban Worm Calculator

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African Nightcrawlers are not intended for vermicomposting.

This is Your Complete "How To"!

The description below should get you well on your way to understanding what the Urban Worm Calculator can do and how it does it.

It may seem tricky at first, but this tool is really easy to use. It can give you basic information like how your worms will mutiply over time. Or it can factor in your planned harvests on a month-by-month basis to include any die offs and what the financial value of your worms may be. For the vermicomposters, it tells you how much food waste you can expect them to process, and what amount of castings you might expect them to produce each day. 

It also allows you to set some goals and it will instantly tell you when you should reach them.


Let's get started!



Settings Area

Unit of Measurement: Makes your units reflect metric or standard.

Currency: Lets you choose one of 8 global currencies.

Basic Input Area


Basic Input Area

Summary: These are the simplest inputs. Once these are filled, a sidebar "Scoreboard" appears (pictured below) and your Results Area becomes partially populated.
Start Date: This is simply the date you assume your worms start multiplying.
Starting Quantity: This isn't really a quantity, but weight.
Monthly Reproduction Rate: This ranges from 0-200 percent but defaults to 25%, which equates to the oft-cited " double every 90 days" statistic. While it is a monthly rate, it compounds daily so assuming no die offs or harvesting, you will get slightly better actual reproduction that the number you enter.   Clicking the orange button will give you the option of entering reproduction rates specific to each month. Note: If you neglect to enter a rate for a certain month, it assumes zero reproduction for that month.



The "Scoreboard"

Advanced Input Area


Advanced Input Area

Quantity Goal: This allows you to set a goal for how many lbs or kg you want to reach. Assuming you entered a Start Date and Starting Quantity, entering a number here calculates the date you will reach that goal, which you will see in the "Scoreboard" that will appear to the right of the screen.
Maximum Surface Area: Enter your best guess of how much surface area you have for vermiculture or vermicomposting.
Population Density: How much worm weight per surface area do you think you'll have? Once you enter that number here, the Scoreboard will automatically show you the month and year you will reach your maximum capacity for vermiculture or vermicomposting.
Worm Unit Retail Value: This is where it gets kind of fun! How much do you think you will be able to sell your worms for per lb or kg? Once you enter a number here, the Scoreboard will show a projected value of what your worms will be worth at the end of the 12th and 24th month from your Start Date.
Castings Retail Value: Same as above except there is no number to look at on the Scoreboard. You'll find a number for Daily Castings Retail Value in the Results Area, which I will describe later.
Monthly Die Off: This allows you to identify a percentage of your worms that you assume will die each month. This also allows a monthly specific percentage.
Monthly Harvest: This field allows you to indicate how much worm weight you'll be harvesting each month. Don't forget to use the monthly-specific option for a more precise prediction.
Inventory Value Goal: This is where to ask the calculator, "When will my inventory reach a certain financial value?"  This is similar to a Quantity Goal, but instead of weight, you are asking for dollars . . or Euros . . or Yen . . .etc.
Sustainable Harvest Goal: This handy feature allows you to enter a desired amount of worms you would like to harvest monthly without reducing your stock from one month to the next. Once you enter a number, the Scoreboard shows what month and year you will reach that goal.
Date to Start Harvest: This date defaults to the current date but allows you to specify when you will start harvesting your worms.
Vermicomposting Efficiency: I give a little love to the vermicomposters here. This number represents the percent of your worms' weight they will eat each day. It assumes you have composting earthworms and defaults to 50% but up to 100% is selectable.
Vermicast Output %: This is the percentage of worm food you assume will be converted to castings. To be honest, this number could be a wild guess, but I set the default to a nice, round 10%.  This number will tend to be low because 70-90% of most food scraps are water weight.

Sidebar "Scoreboard"


The Scoreboard automatically pops up whenever you populate the Basic Input area with your input.


The Scoreboard again

Because your Start Date and Monthly Reproduction Rate are pre-populated with default values, this will appear whenever you enter your Starting Quantity.  Just know that it won't really give you much information until you've entered data in the Advanced Inputs.

Reach Quantity Goal:  Given that you've entered a Quantity Goal, this will tell you what month and year you'll reach it.
Reach Inventory Value Goal:  This is the date when you'll reach the Inventory Value Goal you set in the Advanced Input Area.
Reach Sustainable Harvest Goal: As you can imagine, this tells you when you'll reach your Sustainable Harvest Goal, if you entered one.
Reach Max Capacity: If you entered a Max Surface Area Available and Population Density values, this will calculate when you'll run out of space for vermiculture or vermicomposting.
Worm Retail Value in 12 Months:  If you enter a Worm Unit Retail Value (price per pound/kg), it will tell you the financial worth of your inventory at the end of the 12th month after your Start Date.  Note:  The first month's results are only the results between the Start Date and the end of the month.  This is important because if you run this calculator today and run it again tomorrow using the exact same figures, you will get slightly different numbers as you will be working with one less day.
Worm Retail Value in 24 Months:  Surprise!  This gives you the financial value of your inventory at the end of the 24th month after your Start Date. And this is the most eye-popping display of compounding interest a worm farmer is likely to see.

One note of caution:  This tool does math, plain and simple.  Even though I place default values in Monthly Reproduction Rate and other areas, there are no suggestions here as to what your numbers should be.  Rather, the calculator tells you what your numbers will  be if your assumptions about reproduction rate, harvests, and monthly die off are correct. 

Results Area

This section gives you a 24-month breakdown of your results. Most columns are self-explanatory, but I will explain a little bit of how we came up with the numbers.


Results Area

Month: The first row reflects the end of the current month, not one month or 30 days from the start date.  So if you use the calculator near the end of the month, you are not going to get your assumed Monthly Reproduction Rate since you are now working with just a few days rather than 30.

Qty (Quantity): This reflects the quantity of the previous month plus reproduction minus and harvests and die offs.

Daily Vermicomposting Capacity: Given an entered Vermicomposting Efficiency, this reflects the amount of weight in food or food waste your worms could process each day. Warning: think of this as a weight to work towards as opposed to a weight you can just dump in your bin/bed/flow-through, especially if you have set 100% for Vermicomposting Efficiency. I don't want the Urban Worm Calculator - or me - held responsible for a stinky, overheated bin!

Daily Castings Output:  Given an entered Castings Unit Retail Value, this is the financial value of the worm castings produced that day.

Castings Retail Value: This reflects the value of the castings your worms will produce daily by the end of the month. A future version may include a cumulative value of the castings produced for the entire month.

Worm Retail Value:  This is the total value of your worm inventory on that date.

Sustainable Harvest: This is the worm weight you could harvest each month without reducing your worm stock below the level of the previous month. If you think of this as a financial calculator - and that's pretty much what it is - this is the interest minus any withdrawals in for the form of die offs and harvests from previous months.

Sustainable Harvest Value:  This is the financial value of your Sustainable Harvest.

**See the little question mark?  That can help answer questions too.

Just hover your mouse over anything with a question mark to get a quick description of what kind of information the calculator wants from you.tooltip

Urban Worm Calculator Videos

From beginner to advanced calculations

Part I: Settings and Basic Calculations

Part II: Advanced Input

Part III: Calculating Your Sustainable Harvest