You step on the scale and your trend weight reads 86.4 kg (190.5 lb). A wedding sits in the calendar six weeks away. Picking the goal weight is quick and the date is fixed, but the two rarely fit together.
The short answer: choose a goal weight inside the healthy BMI range for your height, measure your current weekly rate on the trend, and divide the distance to the goal by that rate. The result is your target date. A date you wish for works only as a cross-check: it is realistic when the rate it demands is one you can actually keep up.
The goal weight: a range, not a point
BMI sets the frame. In the CDC adult BMI categories, below 18.5 is underweight, 18.5 to below 25 is healthy weight, 25 to below 30 is overweight and 30 or more is obesity. Your goal belongs inside the healthy range for your height and never below it. To find the range, multiply the BMI by your height in metres squared.
| Height | BMI 18.5 | BMI 25 |
|---|---|---|
| 1.65 m (5 ft 5 in) | 50.4 kg (111 lb) | 68.1 kg (150 lb) |
| 1.75 m (5 ft 9 in) | 56.7 kg (125 lb) | 76.6 kg (169 lb) |
| 1.85 m (6 ft 1 in) | 63.3 kg (140 lb) | 85.6 kg (189 lb) |
BMI knows nothing about muscle mass, age or where your body stores fat. A trained person can feel well at the top of the range. If you are unsure which weight suits you, ask your doctor.
At 1.75 m and a trend weight of 86.4 kg (190.5 lb), your BMI is 28.2. A first goal of 80 kg (176 lb, BMI 26.1) is a concrete step, and 76 kg (168 lb, BMI 24.8) sits in the healthy range. The examples below use 80 kg.
The target date: distance divided by rate
From 86.4 kg to 80 kg is 6.4 kg (14 lb). How long that takes depends only on how much you lose per week:
| Weekly rate | Time for 6.4 kg |
|---|---|
| 0.3 kg (0.7 lb) | about 21 weeks |
| 0.5 kg (1.1 lb) | about 13 weeks |
| 0.8 kg (1.8 lb) | 8 weeks |
Which rate makes sense? The CDC says that people who lose about 1 to 2 pounds a week (roughly 0.45 to 0.9 kg) are more likely to keep the weight off. The rate you already achieve today is the best starting point, because it contains your real routine and your weekends. If the 7-day change of your trend jumps from week to week, average over four weeks: the trend stood at 88.4 kg (194.9 lb) 28 days ago and sits at 86.4 kg today, so that is 2.0 kg in four weeks, or 0.5 kg per week. For help judging the pace, read how fast you should lose weight.
At 0.5 kg per week and a start on 5 October, you arrive after 13 weeks, around 4 January. At 0.3 kg per week it becomes early March.
The wished-for date as a cross-check
Back to the wedding. Six weeks for 6.4 kg demands 1.07 kg (2.4 lb) per week. That sits above the CDC range and above one percent of your body weight, which is 0.86 kg at 86.4 kg. You would struggle to hold that pace.
You have three levers:
- move the date, here to eleven weeks and 0.58 kg per week,
- lower the goal, for example to 82 kg (181 lb): 4.4 kg in six weeks is 0.73 kg per week,
- shift both a little.
The third option is usually the most honest one. A milestone for the event and the final goal afterwards take the pressure off without giving up the goal. Test each proposal by asking which weekly rate it needs and whether you have reached that rate lately.
Reading the question in the trend curve
A single daily value is useless for this calculation. It swings by one to two kilos with water, salt and digestion, and the reasons are laid out here. Any rate taken from two daily values is chance. You need the trend.
Trendcurve calculates the weekly rate by regression over the last 14 trend values. In the Goal tab you set your goal weight and the app shows your progress. You choose a desired pace as an amount per week in kg or lb, and the app warns as soon as the desired pace or the measured rate exceeds one percent of body weight per week. Both are free.
The forecast with target date is a Pro feature. It divides the distance by your measured rate and shows planned against measured, so you see how many days ahead of or behind plan you are. Without Pro, you do the formula above yourself with the rate from your trend. An example: your desired pace is 0.5 kg per week, but the trend shows 0.4 kg, so your target date lands about three weeks later than planned. The forecast card shows that gap as it opens, not on the planned date. How the trend value itself is built is explained in trend weight instead of the daily value.
Where the calculation reaches its limits
Division assumes a constant rate, and the rate rarely stays constant. Going up works the same way with the sign reversed: distance to the goal divided by the measured weekly rate upward. Hall and colleagues describe how body weight responds only slowly to a change in intake, with half-times around one year. In practice, the closer you get to the goal, the flatter the curve becomes, and the last kilo takes longer than the first.
Three consequences for your plan:
- Treat the calculated date as the earliest date, not a guarantee. A buffer of two to four weeks is no weakness.
- Recalculate every four weeks. The date moves with the rate, which is what a forecast is for.
- One or two flat weeks are no failure. A real plateau means a trend that stays flat for three to four weeks.
With medication, an existing condition or a pregnancy, the schedule belongs in a doctor's hands. Trendcurve is not a medical device and gives no recommendations.
To try it today: write down your trend weight, subtract your goal weight and divide the difference by 0.5 kg (1.1 lb). That number is the count of weeks to your first target date. Recalculate in four weeks with the rate you have measured by then.