Investment & Growth

Compound growth, depreciation, and linear growth for financial and business modeling.

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How fast does your retirement fund grow? How quickly does a car lose value? This walkthrough models investment returns, business growth, and asset depreciation using CalcMark’s growth functions.

The complete CalcMark file is available at testdata/examples/investment-growth.cm.

Retirement Savings #

You start with $50,000 in savings, a 7% annual return, and 30 years until retirement. The compound() function models exponential growth over time.

initial_savings = $50000
annual_return = 7%
years_to_retire = 30

retirement_fund = compound $50000 by 7% over 30

Without a frequency modifier, compound() compounds once per year: A = P × (1+r)^t. The 7% annual rate is applied once per year for 30 years, growing $50K to ~$380.6K.

CalcMark features: compound() function for exponential growth; currency literals ($50000); percentage literals (7%).

Monthly Compounding #

Real-world investments compound more frequently than once per year. Adding monthly switches to the financial compounding formula:

A = P × (1 + r/n)^(n × t)

where r = annual rate, n = 12 (monthly), t = years.

retirement_monthly = compound($50000, 7%, 30 years, monthly)

Monthly compounding pushes the result to ~$405.8K – about $25K more than annual compounding over the same 30 years. The frequency adverb (monthly, quarterly, weekly, daily, yearly) is what triggers this formula. Without it, you get simple growth.

CalcMark features: monthly frequency modifier; 30 years unit annotation on the periods argument.

Business Growth #

Growth functions are not limited to money. You can use custom units like customers or users. Here you model a startup’s customer base growing 15% per month over 24 months.

starting_customers = 500 customers
monthly_growth = compound 500 customers by 15% over 24

Starting from 500 customers at 15% monthly growth, you reach ~14.3K customers after two years. CalcMark preserves the customers unit through the calculation.

The natural language form reads like a sentence:

compound 1000 users by 10% over 12 months

Starting with 1,000 users and growing 10% per month for a year yields ~3.1K users. The NL form (compound X by Y% over Z) is equivalent to calling compound(X, Y%, Z).

CalcMark features: Custom units (customers, users); compound natural language form (compound X by Y% over Z); unit preservation through growth functions.

Linear Growth #

Not all growth is exponential. The grow() function adds a fixed increment each period. Here you model adding $200 per month to a savings account over 5 years (60 months).

savings_plan = grow $0 by $200 over 60

grow(start, increment, periods) adds the increment once per period: $0 + ($200 * 60) = $12K. No compounding – just steady accumulation.

The natural language form works with custom units too:

grow 100 subscribers by 50 over 52 weeks

Starting with 100 subscribers and adding 50 per week for a year gives you 2,700 subscribers. The NL form (grow X by Y over Z) is equivalent to grow(X, Y, Z).

CalcMark features: grow() function for linear (additive) growth; grow natural language form; custom units (subscribers).

Asset Depreciation #

Assets lose value over time. The depreciate() function models declining-balance depreciation – each period reduces the remaining value by a fixed percentage.

car_value = depreciate $35000 by 20% over 5

A $35K car losing 20% per year is worth ~$11.5K after 5 years. Each year applies the 20% rate to the current value, not the original price.

You can set a salvage floor with the to keyword. The asset will never depreciate below that value:

depreciate $80000 by 25% over 10 years to $2000

This $80K piece of equipment depreciates at 25% per year but cannot drop below $2,000. After 10 years it lands at ~$4,505 – still above the floor. Without the floor, it would reach the same value here, but the to clause protects against longer time horizons.

Finally, office furniture at a gentler rate:

furniture = depreciate $15000 by 15% over 7

$15K in furniture at 15% per year is worth ~$4,809 after 7 years.

CalcMark features: depreciate() function for declining-balance depreciation; depreciate natural language form (depreciate X by Y% over Z); salvage floor with to keyword.

Features Demonstrated #

This example showcases the following CalcMark features:

• compound() – exponential growth with percentage rates
• monthly – compounding frequency modifier (also quarterly, weekly, daily, yearly)
• compound NL form – compound X by Y% over Z
• grow() – linear (additive) growth with fixed increments
• grow NL form – grow X by Y over Z
• depreciate() – declining-balance depreciation
• depreciate NL form – depreciate X by Y% over Z
• Salvage floor – to $2000 keyword in depreciation
• Custom units – customers, users, subscribers
• Currency literals – $50000, $35000
• Percentage literals – 7%, 15%, 20%
• Markdown prose – headings, paragraphs, and inline comments between calculations

Try It #

cm testdata/examples/investment-growth.cm