The key takeaway
Start with a modest change from estimated maintenance. A larger deficit is not automatically more useful or sustainable.
What a deficit means
If your body uses more energy than you eat over time, you are in an energy deficit. Maintenance is the approximate amount that keeps your weight stable over a longer period. Both can change with your circumstances.
For example, if estimated maintenance is 2,400 kcal, an illustrative 10% reduction gives 2,160 kcal. This is arithmetic, not a personal recommendation or a promise of a particular weekly loss.
Find a workable starting point
Our deficit calculator compares 10% and 15% reductions, capped at 500 kcal/day. These are planning options. They do not establish that a particular intake is appropriate for everyone.
NICE recommends that low-energy diets of 800–1,200 kcal/day are used only within supported specialist or long-term-condition services. This site does not provide those diets.
- Start with the smaller change if you are unsure.
- Keep regular meals and adequate variety.
- Consider how the plan feels on work days and days off.
- Do not automatically subtract calories again when a calculator has already included a deficit.
Use feedback before changing the target
After several consistent weeks, look at the broader weight trend alongside hunger, energy and how manageable the plan feels. One high reading is not a reason to cut food.
If there is no clear trend, first check whether your routine and portions have actually been consistent. A dietitian can help if the pattern is unclear or the intake is becoming difficult to sustain.
Know when to pause
Persistent fatigue, dizziness, feeling cold, distress around food or loss of normal menstrual cycles deserve attention, not a bigger calorie cut. Seek appropriate medical advice.
Intentional weight loss is not suitable for everyone. Pregnancy, breastfeeding, eating-disorder history, low body weight and medical conditions require individual guidance.
Put it into practice
Sources & further reading
These sources support the general information and explain the wider context. Practical examples are illustrative.
Our editorial approachGeneral educational information for adults. Estimates are not a diagnosis or a personalised diet. For pregnancy, breastfeeding, eating-disorder concerns, medical conditions or medication-related questions, seek qualified guidance. Read the full disclaimer.