Insert mandatory complaint about percentages being misused : their point is the approximation : 1.02×1.03~1.05 <=> +2%+3%~+5%, which only holds up to low tens +/-%.

There is a solution for you - log points! https://en.wikipedia.org/wiki/Relative_change#Logarithmic_ch... , http://a-loonie-saved.blogspot.com/2008/08/log-points.html

An example of deceptive arithmetic: A mutual fund's 5-year history of annual returns is −70%, +30%, +50%, +20%, +40%. Naively, the total return for the 5-year period looks like +70%. But in fact it's −1.72%, because the reciprocal function makes the −70% very “heavyweight” compared to the positive changes.

Using log points instead, the 5-year sequence is approximately −120.4, +26.2, +40.5, +18.2, +33.6. The sum of these rounded numbers is −1.9 (nowhere near +60.0), which agrees well with the correct result of about −1.735 log points (i.e. −1.72%).