Formula
Estimated harvest = plants × yield per plant. Example: 20 plants × 2 kg each = about 40 kg. Use a yield you have actually seen for that variety, not a catalogue maximum, or your estimate will be optimistic.
Succession planting (see Succession Planting guide) spreads this harvest over weeks instead of one glut.
How to use it, step by step
Enter the number of plants and the yield per plant in whatever unit you use — kilograms, pounds, or fruits per plant. Use a yield you have actually seen for that variety in your conditions, not a catalogue maximum. The calculator multiplies the two numbers. Then think about timing: a single harvest date gives a glut, while succession planting spreads the same total over weeks. Use the result to decide how many plants you need, not just how many you want.
Worked example in detail
Twenty tomato plants at 2 kg each give about 40 kg. If your household eats 2 kg per week, that is 20 weeks of tomatoes — far more than a single planting will deliver at once, which is why freezing, preserving or sharing is part of the plan for a large planting. Halving the plants to 10 still gives 20 kg, which may be plenty. The calculator makes that trade-off visible before you plant.
What affects real yield
Variety, soil fertility, water, sunlight, pests, disease and harvest timing all change yield. Picking regularly often increases total yield for crops like beans, courgettes and tomatoes, because the plant keeps producing. Leaving fruit to over-ripen on the plant can slow further production. Weather in a single bad week can reduce a season's total more than any calculator can predict, so treat the result as a planning estimate, not a promise.
Frequently asked questions
Why is my yield lower than the packet says?
Packet yields are usually measured in trial conditions with ideal soil, water and spacing. Home gardens rarely match all of those at once. Use your own last season's yield as the input next year for a more honest estimate.
Should I plant fewer plants and more varieties?
Often yes. A smaller number of well-cared-for plants usually out-yields a crowded bed, and variety spreads the risk if one crop fails or is hit by pests.
How do I handle a glut?
Succession planting, freezing, drying, fermenting and sharing with neighbours all help. Planting everything on the same day guarantees a glut; staggering by two weeks avoids it. See the succession planting guide.