What this calculator works out
This calculator turns a basal metabolic rate into a total daily energy figure by applying an activity factor, then adds any adjustment you choose to make.
It shows maintenance — the intake at which weight would be broadly stable — and the adjusted figure separately, so the effect of the adjustment is visible rather than folded into a single number.
Enter your details
Before you rely on the figure
- Calculate your BMR first with the BMR Calculator and enter that figure.
- Choose the activity level honestly. Most people overestimate; a desk job with three gym sessions a week is usually 'lightly active' rather than 'very active'.
- Leave the adjustment at zero to see maintenance. Any change you make should be modest and sustainable.
- This is an estimate with an error of several hundred calories a day for any individual.
BMR equations are reasonably accurate. Activity factors are broad bands covering very different lives, and the gap between adjacent levels is often 250 calories or more. Choosing one level too high is the single largest source of error in this calculation.
How this calculator works
A multiplication and an addition:
Maintenance = BMR × activity factor
Adjusted total = maintenance + your adjustment
1.2 sedentary · 1.375 lightly active · 1.55 moderately active
1.725 very active · 1.9 extremely activeThe activity factors are the standard Harris-Benedict multipliers, used with Mifflin-St Jeor BMR figures throughout. They cover all activity across the day, not just deliberate exercise — a job spent on your feet counts.
The calculator applies no floor and makes no recommendation about what adjustment is appropriate, because that depends on circumstances it cannot see.
Worked example: BMR 1,700, moderately active
Using the default figures — a BMR of 1,700, moderately active, no adjustment:
- Maintenance: 1,700 × 1.55 = 2,635 kcal/day
- With a zero adjustment, the total is the same
Now change the activity level one step in each direction. Lightly active gives 2,338; very active gives 2,933. That is a spread of nearly 600 calories a day from a single dropdown, on identical body measurements — which is why the honest reading of this result is a range rather than a figure, and why tracking what actually happens over a few weeks beats trusting the calculation.
Common mistakes
- Overestimating activity level. The most common error, and worth several hundred calories.
- Entering weight instead of BMR. The first field expects a calorie figure.
- Making a large adjustment. Aggressive deficits are harder to sustain and more likely to be abandoned.
- Treating the figure as precise. The error range is wider than most adjustments people make.
- Double-counting exercise. The activity factor already includes it; adding exercise calories on top counts it twice.
Frequently asked questions
How accurate is this?
Directionally useful, individually imprecise. The BMR equation carries around 10% error, and the activity factor adds considerably more. For most people the realistic accuracy is plus or minus several hundred calories a day. The reliable approach is to use it as a starting point, then adjust based on what actually happens over three or four weeks.
Which activity level should I choose?
Be conservative. Sedentary means a desk job and little deliberate exercise. Lightly active covers one to three sessions a week. Moderately active is three to five. Most people with office jobs who exercise a few times a week fall into lightly or moderately active, not the higher bands. If in doubt, choose the lower one.
Should I eat back exercise calories?
Not if you have used an activity factor, because the factor already accounts for your typical exercise. Adding tracked exercise calories on top counts the same activity twice, and fitness trackers tend to overestimate energy expenditure — sometimes substantially.
Is a calorie deficit the right approach for me?
That depends on your circumstances, health and history, and it is not a question a calculator can answer. A GP or a registered dietitian can give advice that takes account of medication, existing conditions and anything else relevant. The NHS also publishes free weight management guidance and can refer to local services.
Is what I enter stored?
No. Everything is processed in your browser and never transmitted or retained. If thinking about weight, food or body shape is causing you distress, these tools are unlikely to help and may make things harder. Beat, the UK eating disorder charity, runs a free helpline and online support, and a GP can refer you to specialist services.
Related tools
References
- NHS — healthy eating guidance, calorie information and weight management services
- GOV.UK — Scientific Advisory Committee on Nutrition dietary reference values
Sources are checked at publication and can change — how I choose and check references.