MICs can fluctuate dramatically

Last updated on November 30th, 2017 at 02:37 pm

A common assumption vis-à-vis technical debt is that its productivity-depressing and velocity-reducing effects, usually regarded as interest on the technical debt, can be modeled as relatively constant over time. In practice, the magnitude of these effects can vary dramatically with time, and that variation provides planners valuable insight and flexibility.

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, although the rate did fluctuate, it did so in a narrow range of 3.3% to just over 4.5%. When we speak of “interest,” we tend to evoke an impression of relative stability, even when we’re speaking of technical debt, where MICs 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, Buschmann states that the longer we wait to retire technical debt in design and code, the larger the amount of interest [Buschmann 2011]. This presumes constant, or at least non-negative, metaphorical interest charges, an assumption that might be valid for some situations, but which is not universally applicable. Those projects that entail maintenance or extension of parts of the system that don’t manifest a specific class of technical debt, and which don’t depend on elements that do manifest it, are much less likely to incur the MICs associated with that debt. So with respect to any particular class of technical debt, during time periods in which no projects incur MICs, the interest accrued in those periods 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”).

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

Available: here; Retrieved: March 16, 2017.

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[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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