Lifetime Consumption Smoothing
Vary your savings rate by life stage to optimise lifetime, not annual, spending
The standard advice — save a fixed percentage (10%, 8%) of income for your entire working life — sounds simple but ignores the shape of real life. Income rises, families form, kids are expensive, then become cheap, then leave. Forcing a flat savings rate over that path produces feast-and-famine consumption: skint twenties propped up by debt, squeezed thirties with kids, then fat forties and fifties.
Lifetime consumption smoothing flips the goal. Instead of hitting an annual savings rate, you optimise for a relatively smooth standard of living across the whole working life. That definitionally means a variable savings rate: low (or zero) when income is low or family costs peak, high in mid-to-late career when disposable income spikes. The Institute for Fiscal Studies modelled this for the UK and reached the same conclusion as basic economic theory.
The framework also handles the marginal-utility question: an extra £1,000 to a young low-earner is life-changing; the same £1,000 to a mid-career earner with their housing sorted barely registers. Smoothing routes savings to the years where the present-day utility cost is lowest.
- Optimise lifetime spending, not annual savings rate.
- Marginal utility of £1 falls as income rises — save the cheap pounds, spend the expensive ones.
- Variable income should produce variable savings, not variable lifestyle.
- Saving aggressively when broke can be a worse trade than saving aggressively when comfortable.
- A rule of thumb is not a plan; lifecycle context dominates.
- Map your expected income pathSketch realistic income across the life stages you can foresee — early career, family-formation, peak earning, wind-down. The point is shape, not precision.Pro tipUse parents and older colleagues as reference paths; income usually rises faster and lumpier than people expect.
- Identify your high-cost life seasonsMark periods where non-discretionary costs spike — small kids, housing setup, relocations, ageing parents. These are seasons where flat saving rules cause the most damage.
- Set a target lifetime consumption levelDecide what standard of living you want to sustain across decades. This becomes the anchor — savings rates flex around it, not the other way around.Pro tipMost people's actual lifestyle costs are below what they'd guess; check via 12 months of real spend data.
- Vary savings by seasonSave little or nothing during high-cost / low-income years. Save aggressively during high-income / low-cost years to make up the difference and fund the smoothed path.Pro tipAutomate savings increases the moment income rises so the new money never enters lifestyle.WarningDon't let 'I'll catch up later' become a permanent excuse — periodically test the catch-up assumption.
- Re-plan at major life inflectionsRevisit the smoothing every time the income or cost curve changes meaningfully — promotion, baby, house move, career change. The plan should track reality, not the original spreadsheet.
The IFS modelled UK retirement savings paths and concluded the standard 8% flat rule doesn't fit a typical career — broke 20s, kids in 30s, high disposable income in 40s and 50s.
Felix uses the example of a family squeezed by young children. Telling them to still save 8% can be the wrong advice — focusing on the family until kids are older and catching up later is often better.
Felix grounds the framework in standard economics — consumption smoothing is the textbook implication of the lifecycle hypothesis — and brings in the UK's Institute for Fiscal Studies modelling, which shows a flat 8% rule doesn't fit lumpy income paths. He has long been a critic of the 'always save 10%' rule of thumb, arguing it can be flatly wrong for young people with strong rising-income trajectories.