How long to reach your goal weight

The timeline gives a range, not a date

Calculators print a number sharp to the week: 22 weeks. The number is computed correctly, but none of the inputs are that sharp, because basal metabolism is an estimate, daily intake is an estimate, and activity level is a choice squeezed into five coarse rungs. Stack the three margins and what comes out is not a date but a band that can run for weeks.

Five things widen that band and four sit outside the arithmetic: how the goal weight was chosen, how many days of the week the plan is actually followed, how far the logging drifts, how much more the body slows than predicted, and in which week it gets dropped. All five push the same date further out.

The example below stays fixed: a man of 175 centimetres, 95 kilograms, 40, at a desk. His basal metabolism is 1,849, his maintenance level 2,219. On a 500 calorie deficit he eats 1,719 and wants to lose 10 kilograms. On paper, 22 weeks.

The goal weight itself is half the answer

The answer depends on a number chosen before the question was asked: the goal weight. It is usually picked at random.

The healthy range is a BMI between 18.5 and 24.9. At 175 centimetres that means 56.7 to 76.3 kilograms — a band roughly 20 kilograms wide. Which end of it you aim at takes the weight to lose from 19 to 38 kilograms and, for the same person moving at the same pace, creates the difference between 38 weeks and 76. Nine months.

Picking the bottom end carries no health advantage. The whole band counts as healthy, and sitting near the top gets there in less than half the time.

The plan runs five days a week, not seven

This is the timeline’s largest single distortion. The arithmetic assumes the 500 calorie deficit holds on all seven days.

The same plan yields three different dates. Followed seven days, the weekly loss is 0.45 kilograms and 10 kilograms takes 22 weeks. If two weekend days come out neutral, the loss drops to 0.32 and the timeline stretches to 31. If those two days each run 500 calories over, the loss falls to 0.19 and the answer becomes 51.

The only thing that changed is how many days of the week were counted. The date doubled.

The reason this drift stays invisible is simple: logging on five weekdays and letting it go at the weekend is a common habit, so the average the app displays genuinely does read 1,719 while the weekly total sits elsewhere entirely; the scale follows the weekly total.

This is not a ban on weekends. Building the sum across seven days and giving the weekend a share holds up better: 600 on weekdays and 200 at the weekend produces the same weekly total and is far easier to keep.

Logging error is bigger than formula error

Logging accuracy matters more than the calculator’s estimation error. Studies measuring the intake of free-living people find a gap of 20% to 30% between what is logged and what is eaten, and it comes not from bad faith but from portion estimates, oil in the pan, drinks and tasting bites. In a well-known 1992 study of a small group calling themselves diet-resistant, participants under-reported intake by 47% and over-reported activity by 51%.

In the worked body a 20% shortfall means a day believed to be 1,719 calories is really 2,060. The deficit drops from 500 to 160. The 22-week timeline becomes 68.

Closing a gap that size is not a matter of dieting harder. Weighing what you log for a few days shows where the estimate drifted, and once is usually enough.

The nastiest part of logging error is that it grows. Everything gets weighed in the first weeks, then portion estimates loosen, oil and sauce stop being counted, drinks fall off the record, and by the fourth month the same person using the same app logs a few hundred calories a day short. That is also the stretch where the scale stalls.

The body slows a little more than predicted

The timeline already computes maintenance falling as weight falls. Measurements add a small margin on top: compared with someone of the same body composition who never dieted, a body that has lost weight spends 50 to 100 fewer calories a day.

The extreme case was published in 2016. Contestants on a television competition who lost a great deal of weight very fast were measured six years later: resting expenditure came out around 500 calories below what their body composition predicted. An ordinary deficit does not produce that scale, but the direction is the same.

In the worked body a 100 calorie margin turns the 500 deficit into 400 and moves 22 weeks to 28. Nothing is broken. There is simply a body running more economically than the arithmetic assumed.

Do not build a date out of the first fortnight

A 500 calorie deficit predicts 0.9 kilograms in two weeks. The scale usually shows 2 to 2.5, because much of what leaves in the first days is glycogen and the water bound to it.

That is not the problem; carrying that rate forward is. Someone down 2.5 kilograms in a fortnight builds the timeline in their head around 1.25 a week and expects 10 kilograms gone in eight. The real answer is 22 weeks. When week five falls behind, the plan gets blamed — though it is working, and what is wrong is an expectation manufactured out of the first fortnight.

The fast plan you drop is slower than the slow one you keep

Two plans, same person. The first runs a 750 calorie deficit at 0.68 kilograms a week, dropped in week six: 4.1. The second runs 350 at 0.32 a week for forty weeks: 12.7.

By week forty the gap is over 8 kilograms. The fast plan’s weekly rate was more than double.

The question when picking a timeline is not which pace finishes sooner but which pace survives forty weeks. Those are not the same question, and calculators answer only the first.

Arriving is not the end of the plan

When the worked body reaches 76 kilograms, maintenance drops from 2,219 to 1,991. Same person, same activity level, 228 fewer calories a day.

Going back to the pre-diet plate brings the weight back. A new maintenance level comes into force on the day you arrive, and the timeline’s real finish line is not there but in the first six months at that level.

Accounting for this changes how you pick the pace: the habits built across a slow forty-week plan already teach you to live close to the new maintenance level, while a fast plan dropped in week six leaves you, on the day you arrive, alone with a calorie level you never learned. The difference between the two plans carries on after arrival.

The weight loss timeline draws both scenarios side by side and says whether the goal is reachable. Where your goal falls inside the healthy band comes from the ideal weight calculator. The maintenance level you build the deficit on comes from the calorie calculator.