Forecasting your sales goals is a bit of an 'educated guess'. No one knows exactly what their sales are going to be.. but the more experience you have - the better you get at guessing.
If you're just starting your budget - don't worry about this too much yet. When you're finished your budget - you'll know whether your goals are high enough to be profitable - or so high that they're unrealistic. In the meantime, just keep these tips in mind:
- Be realistic - falling short of your sales goals will mean falling short of your profit goals too. You don't want that.
- Don't be too pessimistic - If you're too conservative, your overhead markups will end up high - as you'll try to recover all your overhead on a small sales goal. This will make your pricing more expensive than it needs to be.
Do your best to set a realistic target, then finish your budget. When you review your forecast Profit / Loss at the end, you'll be able to dial in your sales goal much more accurately.
... then you just have to hit those goals!