MICs can fluctuate dramatically

Last updated on July 8th, 2021 at 11:54 am

A common assumption vis-à-vis technical debt is that we can model its productivity-depressing and velocity-reducing effects. We model them as the “interest” on the technical debt (MICs). And we assume that MICs are relatively constant over time. In practice, MICs can fluctuate dramatically. Those fluctuations provide planners valuable insight and flexibility, if they choose to use it. Unfortunately, most plans I have seen make the assumption that MICs are relatively stable.

An example of MICs behavior

30-year average fixed mortgage rates in the United States, 2012-2017
30-year average fixed mortgage rates in the United States, 2012-2017, in %. Over this five-year period, rates did fluctuate. But they did so in a narrow range of from 3.3% to just over 4.5%. When we speak of “interest,” we evoke an impression of relative stability. This happens even when we’re speaking of technical debt. MICs for technical debt can vary from 0 to well above MPrin in any given time period. That’s one thing that makes the term “interest” so misleading in the context of technical debt. Data provided by U.S. Federal Reserve Bank of St. Louis [Federal Reserve 2017].
As an example of this assumption is available in a paper by Buschmann [Buschmann 2011b]. He states that the longer we wait to retire technical debt in design and code, the larger the amount of interest. This presumes constant or non-negative MICs. That assumption that might be valid for some situations, but it isn’t universally applicable.

Consider a project that entails maintenance or extension of parts of the system that don’t manifest a specific class of technical debt. And suppose that the assets in question don’t depend on elements that do manifest that debt. Such a project is less likely to incur the MICs associated with that debt. So with respect to any particular class of technical debt, there might be time periods in which no projects incur MICs. During those periods, the interest accrued can be zero. In other time periods, the interest accrued on account of that same class of technical debt could be very high indeed.

These effects are quite apart from the tendency of MPrin to grow with time, as we noted in an earlier post (see “Debt contagion: how technical debt can create more technical debt”).

Last words

A capacity for projecting MICs associated with a particular class of technical debt can be useful to planners as they work out schedules for maintenance projects, development projects, and technical debt retirement projects. Technical debt retirement projects are also subject to MICs, including from classes of technical debt other than the debt they’re retiring.

Analogous to the functioning of governance boards, a technical debt resources board could provide resources for evaluating assessments of likely MICs for maintenance projects, development projects, and technical debt retirement projects. Decision makers could use these assessments when they set priorities for these various efforts. I’ll say more about technical debt resources boards in future posts.


[Buschmann 2011b] Frank Buschmann. “To Pay or Not to Pay Technical Debt,” IEEE Software, November/December 2011, 29-31.

Available: here; Retrieved: March 16, 2017.

Cited in:

[Federal Reserve 2017] Federal Reserve Bank of St. Louis. “30-Year Fixed Rate Mortgage Average in the United States (MORTGAGE30US).” Weekly time series.

Available: here; Retrieved: November 25, 2017.

Cited in:

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