The computation of the estate tax is very complicated. You can go to the assessment section of the BIR for assistance. You mentioned that your grandfather left real properties, the gross estate shall include Fair Market Value (FMV) of the real properties as determined by the Commissioner OR the FMV shown in schedule of values fixed by the assessors, whichever is HIGHER. To get the net estate, we deduct from the gross estate the deductions.
the deductions from gross estate includes the following:
1) Expenses, Losses, Indebtedness, and Taxes:
(a) actual funeral expenses or five percent (5%) of the gross estate whichever is lower (not exceeding P200,000)
(b) judicial expenses of the testamentary or intestate proceedings
(c) claims against the estate
(d) claims against insolvent persons included in the gross estate
(e) unpaid mortgages or indebtedness upon property
(f) unpaid taxes
(g) losses incurred during the settlement of the estate
2) Transfers for Public Use-to the government of the Republic of the Philippines or any political subdivision thereof, exclusively for public purposes
3) Vanishing deductions
4) Family Home
5) Standard Deduction -- P1,000,000
6) Medical Expenses
7) Amount Received by Heirs under RA 4917
Net Share of the surviving spouse in the Conjugal Property
You better bring the titles and tax declaration of the real properties to the BIR. They will give you an idea how much u should pay