Hi WneverLOSE
The traditional method is to use a 2-step (or multi-step) model where you assume different growth rates at different times in the future.
STEP 1: assume future growth periods
So you might fx assume that your 30% grower can keep up that rate for 4 years, then dropping to 15% for 10 years and then dropping to 3% from that time onwards.
STEP 2: assume future margins and ROE/ROIC
You then think about the future ROIC: will it increase, decrease or remain stable? If you have some operational leverage the ROIC might increase over time as your margins expand. If you assume competitors come gunning for your business then it might fall. Etc. Map this out along a timeline as well for each of your growth periods.
STEP 3: assume future capital structure and cost
Estimate/think about what future capital structure the company might use. Look at sector examples and estimate the cost of debt as it is (there is a lot of techniques involved in optimising WACC. Google is your friend).
STEP 4: Calculate required reinvestment rate
Given earnings and perhaps a leveraged capital structure you can now calculate the needed reinvestment rate. 30% growth assuming a stable 30% ROIC and no debt is = 100% reinvestment rate. A 15% growth rate at a 30% ROIC is a 50% reinvestment rate and so on. New debt naturally detracts from required reinvestment but lowers net margins due to interest expense. Given your Growth Timeline, your ROIC Timeline and your Capital Structure Timeline then the Reinvestment Timeline becomes calculable.
Step 5: calculate net earnings for each year and discount back to today
Pretty straight forward I hope, but given profit, debt and reinvestment you have excess earnings available, the present value of which is the value of your company. There will be more earnings available in the future but it will be discounted more.
Step 6: apply a margin of safety.
As you can see there are LOTS of assumptions in all the above steps. No way around this: better make them explicitly than hidden back in the dark recesses of your mind. Be critical of course. Generally the triad of Growth-Risk-Reinvestment has to add up: if growth and reinvestment is assumed high but risk low you really have to know why this is so (and vice versa around the triad).
The margin of safety then is applied ON TOP of your conservative estimates.
Then compare to price and buy if appropriate :-)
Voila!
/Ulrik