What the rule is trying to do
The familiar framework separates needs, wants and saving or debt goals. Its real value is not the exact percentages; it reminds you that current life and future goals must share the same income.
Your costs may be different
Housing, family responsibilities and location can make essential costs much higher than a textbook percentage. Measure your current ratios first and improve gradually instead of treating a different ratio as failure.
Give saving a purpose
Your savings share can include an emergency fund, a planned purchase, investing or faster debt reduction. Different stages of life need different priorities, so the percentage can move while the habit remains.
Use ratios as a dashboard
If a percentage changes for several months, investigate why. Ratios are useful when they help you notice a trend and make a better decision, not when they become a grade.